5 Slack alternatives for internal corporate communication

Slack is one of the leading group software applications. Shortly after it was launched, it already had hundreds of thousands of users. In September 2017, more than six million people were using the platform daily. Stewart Butterfield and his team began developing the collaboration tool on the side while programming an unfortunately unsuccessful game. The fact that the team of developers used the application themselves played a large role in the user-friendly aspect of the tool. In 2015, however, it became clear that the new-to-the-scene software was unfortunately not perfect: Slack suffered a hacker attack, in which a large number of users’ data was compromised. As a result, the company quickly increased security standards and introduced a two-factor authentication system.

Given the growing popularity of the cloud-based software, attacks may occur again in the future. For many users, this is the main reason for considering alternatives to Slack. Slack is a cloud-based software with US-based servers. It’s not possible to self-host sensitive company data, which is a major disadvantage to some companies and a large factor in the search for Slack alternatives.

What can Slack do?

Before researching Slack alternatives, it’s a good idea to look into what makes Slack so popular and which features its competitors have to compete with. First of all, the communication tool is a streamlined solution for companies that don’t wish to host project collaboration and document sharing themselves. The installation process is quick and easy. All you need to provide is information about your industry, the number of employees and your role in the company. With this information, Slack will optimise its user interface. Lastly, select your domain based on your company name.

The core of Slack is the channel. Chatrooms can be created for any important projects or teams. Team leaders can simply add people to a specific channel and edit the access permission accordingly. The software places particular emphasis on team discussions, which, in turn, helps increase transparency within the company. The search function adds to the practicality of the tool and allows users to quickly search all group discussions, private messages, and uploaded files. Commenting on documents stored directly in the cloud is just as easy. Important conversations can be pinned to the top of the tool. As of September 2017, communication between companies and teams is now possible.

Chatbots also enhance the functionality of the tool. As seen in the above image, a chat with the “slackbot” can be found under “direct messages”. The bot will answer all questions about using Slack and often refers users to the relevant articles. The “polly” bot is there to assist users in creating polls.


Since September 2017, Slack supports German, Spanish, and French. Japanese will be added soon.

Slack itself has no content management functions but it has integrated a range of apps that users often work with. Slack expanded its cooperation with Google and offers apps for linking to Google Drive, Hangouts, and Calendar. Zoom provides Slack’s missing video meeting feature. Other integrated apps are:

  • Zendesk
  • OneDrive
  • Dropbox
  • RSS Feed
  • Twitter
  • Salesforce
  • Asana

The simple and intuitive user experience makes Slack a very popular choice. Read through our detailed article on the topic to find out more about Slack. Here you can learn all about using Slack to lower the amount of company e-mails, save energy, and improve transparency within your company.

The best Slack alternatives

Nevertheless, data protection and security remain important arguments against the popular chat program. We introduce you to the best Slack alternatives – some are free of charge and others come at a cost. Depending on which aspects of your company’s internal communication are most important, some of the programs in the below list may be of interest to you.

Spike: The Innovative Slack Alternative

Spike is rethinking the way teams communicate. Today’s modern companies still do plenty via email. But, especially in the case of longer conversations, it’s difficult to maintain an overview and follow the discussion when using more traditional email programs. The Spike app presents email conversations in a format we tend only to associate with messaging and chat programs: a dialogue-based presentation. The app does away with subject lines and signatures. Users can use their email as they would a chat, allowing them to communicate naturally.

In order to protect your privacy, the video will not load until you click on it.

The benefit of Spike is that it doesn’t require its own account. Instead, the program works by accessing your already existing e-mail account. Those who have a free e-mail account with providers like Gmail or Yahoo and work with fewer than 100,000 e-mails can use Spike for free. Professional teams with their own e-mail domains must subscribe to a paid Pro Account, however.  

The program offers more than just a new way of reading your e-mails. Like many alternatives to Slack, Spike does much more to support communication and collaboration within a team. Group chats and sending data are a given, as are video calls. A calendar can also be made use of via Spike. 


One special feature that adds extra security: Messages that are exchanged via Spike can be encrypted. This technology works for communication between Spike users as well as for e-mails sent to others.

Spike can be used on different platforms. Next to Windows and macOS, there are mobile versions available for Android and iOS, as well as one for your web browser.



✔ Video and voice calls

✘ Integration with other apps not possible

✔ Many features included in the free version


✔ Uses existing e-mail accounts


✔ Advanced search function


✔ Clear overview


Fleep: the European cloud


Fleep is a cloud-based, open communication platform. The start-up behind the software is based in Estonia and the team of developers already have relevant experience working on the renowned Microsoft service known as Skype. The cloud server has an Amazon EC2 data center in Dublin. The application began in 2013 and now functions with Mac, Linux, and Windows operating systems, on both web browser and desktop. Users can access the messenger service on the go with the iOS and Android app.

The free version is free for everyone and comes with a large feature package. The business version, on the other hand, allows you to set up an administrator account with which you can, for example, create chat rooms and invite users. The platform allows you to conduct conversations and chats from within the internal communication with external teams and companies – even addresses without a Fleep account can write directly in a chat window and will receive your messages as e-mails. In this way, Fleep tries to shorten communication channels without denying companies their familiar structures.

The free version allows for an unlimited number of users and conversations. In comparison to Slack, Fleep doesn’t limit the number of messages stored. Users can find all archived projects or team chats by means of the search function. Files can be uploaded to a conversation with one simple click and tasks can be easily set and managed. Additionally, marked messages as well as file uploads can be found in the side bar. Each account has 10 GB memory for files or documents.

App integration is unlimited. In addition to the usual cloud services, e-mail and project management tools are available. The ‘appear.in’ plugin supplements the text-based chat system of the Slack alternative with audio and video call functions. Use the Fleep API to integrate larger applications or custom apps.

The business version is only available with subscription but at a reasonable price. The file storage capacity is up to 100 GB. Further features include:

  • Manage accounts, chats, and teams as administrator
  • Company name in profile
  • Company logo for all subusers of the tool

In account management, you can suspend or delete spammers and inactive users.

Advantages Disadvantages
✔ Business account: own company logo and name in tool ✘ Limited file storage, also in business version
✔ Voice and video call integration ✘ No self-hosting possible
✔ Free version allows unlimited message storage and integration  
✔ Cross team and cross company communication  
✔ Cloud server in Dublin  

Rocket.Chat: open source software on the heels of Slack

Rocket.Chat is a free open source alternative to Slack. The messenger software arrived on the market in 2016 and records some of the largest membership numbers within the GitHub developer community. In the wake of Slack’s groundbreaking success, many programmers felt the need to develop a better open source version. The result is quite impressive, but a few initial bugs have not yet been ruled out.

The program stands out amongst the alternatives to Slack because it’s not only free of charge, but also, thanks to open source code, is easily customisable for developers within your company. For large companies that need tech support, there are also fee-based variants. In the basic version Rocket.Chat only provides the application, the hosting is done by each team itself.

Users only need to download the server and sensitive data can remain on their own server. For those that do in fact want a host, Rocket.Chat offers a free, scalable cloud service.

Rocket. Chat offers three packages – Bronze, Silver, and Gold. The price includes between 1 GB and 20 GB storage space an unlimited number of users.

Basic support is also provided with each package. To get priority support however, users must pay extra, also in the cloud version. For larger companies, the monthly fee is often worthwhile, but smaller companies may prefer the basic support.

Rocket.Chat offers the normal messenger features that every good Slack alternative should provide. Team and project-related chats are possible, as well as private messages. Private channels, as seen above, are closed channels with extra encrypted content that’s not archived. Additionally, Rocket.Chat adapts to different user types. The in-house company communication functions just as fluently as Rocket.Chat’s integrated B2C live chat on your website. You can add an unlimited number of users, guests, and channels. All messages are end-to-end encrypted. Two-factor authentication for file sharing provides additional security.

The developers are constantly working on the Rocket.Chat code, which enabled them to implement the API into the core software. Use Hubot and Webhooks to integrate the existing tools and other Rocket.Chat bots. The community recommends, for example, Jitsi Video Bridge to stabilise the existing video chat and connect the geographically distant chat partners. Further integrations include:

  • Google Calendar
  • DeadSimpleScreenSharing
  • Azure Alerts
  • BitBucket
  • Jira
  • PagerDuty
  • Nixstats
  • Travis CI
  • Trello
  • GitHub and GitLab
  • Zapier

Rocket.Chat is ahead of Slack in terms of its voice and video call function. During a meeting, chat participants can easily join the conversation and get access to the screen sharing option.

The typical conversation chaos that comes about with long chats is organised by Threads and Hubot – though this is less mature than the Slack model, the slackbot.



Supports 50 languages with automatic real-time translation

Priority support with monthly costs

Distinguishes between B2B and B2C chat


Easy to install on existing infrastructure


Mattermost: your data remains safe on your own server

Mattermost is another open source solution for internal communication. This platform can be hosted on one’s own server or in a private cloud behind your firewall. This way, you retain full control over sensitive data. The Slack alternative can be easily integrated into your existing on-site infrastructure. Even if you’re already hosting your processes on a public cloud, Mattermost can simply be added to your environment. Users praise the tool’s hassle-free scalability. The number of users is limited only by the respective server. Even for companies that have given up their company licence, employees can still use all features of the free Team Edition.

Mattermost is another open source Slack competitor that wants to do things better. The company specialises in secure company communication. Those that need to comply with strict security and compliance standards will often find it easier to keep all data on their own server. To do this, select your server during installation and specify the domain. Then specify whether the program is allowed to send push messages, check spelling, or start automatically every time it boots.

The messenger has a free team edition and two enterprise versions. The enterprise edition E10 is optimised for teams and departments that want more control of their IT infrastructure. Multi-factor authentication, encrypted push notifications, and AACP ensure high security standards. There is a monthly fixed price for the service that is half the price of Slack’s standard version. E20 is an enterprise version with extra compliance and security functions; a few of these functions can be removed from the cost estimate if you don’t need them and others are fixed parts of the offer.

They cover the following areas:

  • Extended compliance support
  • Additional authentication
  • Extended support for your data centre
  • Company analysis

The team edition offers a practical messenger for private clouds; it includes all basic functions of the enterprise edition. Even with the free version, users can benefit from constant improvement updates.

In the program, you can create teams for the corresponding user and each channel allows you to chat about a specific topic. The thread structure clears up long conversations. The search function displays not only the desired message, but also its conversation environment. The taskbar allows users to upload files and search archived documents. From within the chat, users can see when a conference call is taking place and can join the call by accepting the invitation. A calendar entry will be created for this beforehand. In addition to private messages, the VoIP tool enables instant messaging calls and video conferences.


Use the community to request feature enhancements. There are plenty of developers on the community that are usually happy to help.

Unlimited integrations can be added to the team version. However, in terms of usability, Slack has the edge with a simple one-click installation process, whereas Mattermost must be installed manually. While Slack limits bots and apps to 10, Mattermost is unlimited. Also, Slack limits the number of archived messages to 10,000, and Mattermost is again, unlimited. The web version, the desktop application, and the smartphone app all support over a dozen languages – and this number is rising.

Advantages Disadvantages
✔ Individual security standards because you use your own server ✘ Multi-factor authentication is only available in enterprise edition
✔ Multilingual user interface ✘ Audio and video call still in beta
✔ Link preview ✘ No 1-click app integration as with Slack
✔ Open source code for maximum adaptability  
✔ Good scalability  

Microsoft Teams: good integration for Microsoft 365 users

Microsoft Teams is a new messenger tool that is part of the Microsoft 365 Apps for business Suite. When Qi Lu, EVP of Microsoft’s applications and services group wanted to buy Slack, Microsoft founder Bill Gates had other ideas. Instead, he wanted to develop a new version of Skype for Business as an alternative to Slack. Microsoft announced the project at the end of 2016. At the annual Microsoft Ignite conference in September 2017, it quickly became clear to the company what its users had already noticed in Skype for Business: Microsoft Teams had replaced the new version of Skype. In turn, Slack intensified its cooperation with Google.


EVP (Earned Value Professional) is a certified title that was founded in 1956 by the Association for the Advancement of Cost Engineering (AACE International). The certificate is awarded to specialists in value-added management. To do so, you must meet certain ethical standards, pass a test, and have several years of education and work experience.

Following offers from the likes of Yammer and Skype for Business, Microsoft developed the Slack alternative Teams that promised to challenge the competition. While Yammer is best suited to larger companies, Teams is best for companies with a maximum of 1,000 employees. Another special feature: as part of the Microsoft 365 Suite, the Teams platform is one of the few options that users cannot download and use as a stand-alone package. To test the program, a Business Suite is required. The advantage of this is that Teams is fully compatible with all Office applications. Visit the Microsoft Teams website for a free Microsoft 365 Apps for business trial.

Microsoft celebrated the success of Teams at the Ignite conference. According to the software giant, just six months after the soft launch, 125,000 companies were already using the communication tool. This surge in popularity begs the question, is Teams the best Slack alternative? Perhaps the positive numbers are simply because Team Messenger is already included for Microsoft customers.

While much criticism has been voiced about Microsoft’s updates, there is little to fault with Messenger. The software has all the essential features such as chat and instant messages. The HD video calls can host up to 250 people. With guest access, you can also invite people outside of your company to work together in teams. The Outlook calendar integration was lacking during its initial phases but has since been added by developers. Here, your team will receive notifications about upcoming meetings that have been arranged via Microsoft Teams.

Files can be shared in chats or instant messages via the OneDrive cloud. Teams encrypts the documents end-to-end and protects your identity with multi-factor authentication. When sharing files on one channel, the program places them in the shared SharePoint folder for all team members.

In addition, voice call functions like meetings and VoIP are included. On top of this, the software will support calls to phones and will provide a telephone number for the various channels. The program also includes a task manager to improve workflow optimisation.

Chatbots can be added via the app store: simply click on the ‘Apps’ button and choose the tab ‘Bots’. The bots answer questions, provide on-the-spot assistance, and take care of updates. In the store you will also find ‘Connectors’, the Microsoft 365 API for third-party apps such as Adobe Creative Cloud, RSS feeds, Asana, or project management apps such as Aha!.


Microsoft Teams is a special case among the Slack alternatives, as it’s only available in an Office package. One advantage is that missing applications such as a project management tool are supplemented with other Office apps. After future upgrades and enhancements to the still somewhat unfinished application, it could develop into a very good messenger service. If you already own Microsoft 365, it might be a good idea to keep an eye on the developments of Teams.

Advantages Disadvantages
✔ Stable integration with all Office programs ✘ Only available with Business/Enterprise/Education packages of Microsoft 365
✔ Microsoft 365 security standards and professional-level certificates ✘ Many features not yet ready for use
✔ Clear, customisable menu ✘ Lack of privacy: Microsoft scans files for OneDrive

Summary: find a Slack alternative that suits you best

There are many software offers for internal communication, and Slack has been ahead of its competitors for several years. The company has become renowned for its user friendliness, efficient team communication, and improved workflow through increased transparency. However, the best Slack alternatives are in no way inferior to the popular messenger. Mattermost and Microsoft Teams also hold security certificates for companies that comply with strict security standards. Thanks to its innovative email management, Spike is a great alternative to Slack.

Amongst the free alternatives to Slack, the open source software Rocket.Chat leaves room for developers to experiment. Additionally, both Rocket.Chat and Mattermost can be self-hosted on their own server, ensuring you have full control over your data. For those who want to take messenger and hosting into their own hands, Fleep is a good alternative. If you’re not sure which application is right for your business, make sure to try out the free trial version first.

Slack alternatives at a glance






Cloud-based team communication software

Cloud-based communication platform

Open source communication freeware


Free; subscription with free 30-day trial period

Free; subscription with free trial period; a cost estimate for up to 50 users

Freeware; subscription with costs for cloud usage (discount for NPOs and education institutes)

Operating system

macOS, Windows (32 and 64 bit), Linux, iOS, Android

macOS, Windows (32 and 64 bit), Linux, iOS, Android

macOS, Windows, Linux, Android, iOS

Desktop version

Mac, Windows, Linux


Mac and Windows

Suitable for

Start-ups to large businesses

Self-employed, start-ups, SMEs

SMEs, large businesses


Private message

Audio or video Messages

Yes, for meetings

Direct in messenger

Yes, plus add-ons

Data upload

Stride Free: up to 5 GB;

Stride Standard: unlimited

Fleep free: up to 10 GB;

Business: up to 100 GB

Own server Rocket.Chat cloud: up to 50 GB, 1 TB or 5 TB

Search function


All Atlassian products, Giphy, GitHub, Trello

E-mail, cloud (Dropbox etc.), GitHub, Atlassian

 applications, Fleep API etc.

E-mail, GitHub, Trello, Zapier, Bitbucket etc.

Customise access rights

For groups and file sharing

In business version

As administrator

Real-time synchronisation

Special features

Collaboration tools, focus mode

Chat in tool with email contacts

Link preview,

B2C live chat for your website


Documentation, forum, system status, FAQs, technical support

Starter guide, documentation, FAQs, email support

Webinar, documentation, chat, priority support subscription



Microsoft Teams



Self-hosted, open source team communication software

Cloud-based team communication software

E-mail tool and communication platform


Freeware; subscription with free trial period and test server, individual cost estimate for larger customers

Integrated into Microsoft Office Suite for Business (Essentials & Premium) Enterprise (E1, E3, E5) and Education (free), see prices there

Free; subscription for professional users

Operating system

From macOS 10.9, from Windows 7, Linux and Ubuntu 14.04, from Android 5.0, from iOS 9

Windows, macOS, iOS, Android, Windows 10 mobile, Windows Phone 8

Windows, macOS, iOS, Android, web browser

Desktop version

Mac, Windows, Linux (Beta)

Windows, Mac

Windows, Mac

Suitable for

Teams, large businesses with strict security standards

Medium to large businesses of up to 999 employees

Start-ups to large companies


Private message


Audio or video Messages

Yes, for meetings

Yes, for meetings of up to 250 employees

Directly in messenger

Data upload

Depends on the server

With OneDrive

Business: 1 TB;

Enterprise: unlimited


Search function

Search for complete Office Suite



For private cloud/on-site infrastructure & public cloud (with Zapier): Box, Jira, WordPress, Office, PagerDuty etc.

All Microsoft 365 apps, integration with SharePoint


Customise access rights

Can be set in the settings for admins and/or team members

Multiple administrators, can become complicated with large companies


Real-time synchronisation

Innovative presentation of e-mails

Special features

Multi-platform support

Full Microsoft-Microsoft 365 integration

E-mail support, FAQs


Help centre, forum, documentation, technical support, contact forms

Demo video, fast track centre, web and telephone support, FAQ


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