Slack is the default team chat, and it is also a bill that grows with every new member. For small teams, the free plan's 90-day message history limit is the real pain: search stops working, decisions vanish, and the team starts re-asking questions that were answered months ago. Self-hosted Slack alternatives solve this by keeping your messages on your own server, with no per-user fee and no history limit. In 2026 the options are mature enough for a small team to switch without losing the features that matter.

Mattermost: The Closest Slack Replacement

Mattermost is the most direct Slack alternative: channels, threads, direct messages, file sharing, integrations and a familiar interface, all open source and self-hosted. Its free Team Edition covers unlimited users and unlimited message history, which is exactly what Slack's free plan withholds. It runs in Docker with a single compose file, and the mobile apps are solid. The trade-off is that you manage the server, including backups and updates, and some advanced features such as compliance tools sit behind a paid edition. For a small team that wants Slack without the bill, Mattermost is the default answer.

Rocket.Chat, Zulip and the Other Contenders

Rocket.Chat is the most feature-packed option, with video calls, live chat widgets and omnichannel support built in, which suits teams that also talk to customers. Its community edition is free and self-hosted, though the interface is busier than Mattermost and the project has shifted some features to paid tiers over time. Zulip takes a different approach with topic-based threads inside channels, which is genuinely better for teams that discuss several subjects in one channel and hate losing track. It is open source, light on resources and easy to host. Matrix, through the Element client, is the decentralised option: federated, encrypted and free, though the setup is heavier and the interface is less polished. For most small teams the choice is Mattermost for familiarity, Zulip for threaded discussions, or Rocket.Chat for the extra features.

How to Switch Without Losing Your Team

Backups: The Part Everyone Forgets

A self-hosted chat system is only as good as its backups, and this is the part most teams skip until the day the server dies. Set up automatic daily backups from the first day, and store them somewhere other than the server itself, such as an object storage bucket or a second VPS. Test the restore process at least once, because a backup you have never restored is a hope, not a plan. For Mattermost and Rocket.Chat, the database holds everything that matters, so a nightly database dump plus a copy of the file uploads is usually enough. Keep at least thirty days of backups, and document the restore steps in the same place as the admin password, so anyone on the team can recover the system if you are away. A chat system without backups is a single hard drive failure away from losing your team's entire history, and the fix takes less than an hour to set up.

Migration is the part teams fear, and it is simpler than it looks. Export your Slack history before it expires, because the 90-day limit means old messages disappear from the export too. Import what matters into the new system, or archive it as a searchable file and start fresh. Run both tools in parallel for two weeks so nobody is forced to switch overnight, and move one channel at a time starting with the least critical. Host the new system on a small VPS or a free-tier cloud instance, set up automatic backups from day one, and document the login in one place. The savings are real: a team of ten on Slack Pro pays over a thousand dollars a year, while a self-hosted alternative costs the price of a small VPS. The messages stay yours, the history never expires, and nobody can change the pricing on you.