3 Free & Open-Source Slack Alternatives
Slack's free plan quietly limits searchable message history to the last 90 days, and per-seat pricing adds up once you're past a handful of people. Self-hosted team chat removes both limits — full history, no seat cost — in exchange for running the server yourself.
The best Slack alternatives
Rocket.Chat
Our top pickOpen sourceSelf-hostedA full-featured, self-hosted Slack-style chat platform.
Rocket.Chat is the most Slack-like of the three in look and feel — channels, threads, DMs, integrations — and adds compliance and security controls (audit logs, data retention policies) that matter more to regulated industries than a typical small business.
- Channels, threads, and direct messages
- Video calls and screen sharing built in
- Extensive integration and bot ecosystem
- Self-hosted with full message history retention
Mattermost
Open sourceSelf-hostedDeveloper-friendly team chat with deep tool integrations.
Mattermost is particularly popular with engineering teams for its tight integration with dev tools (GitHub, Jira, CI pipelines) alongside standard channel-based chat — a natural fit if your team already lives in developer tooling.
- Channels, threads, and searchable full history
- Deep integrations with dev/DevOps tooling
- Playbooks for structured incident/process workflows
- Self-hosted, with an enterprise tier for larger teams
Zulip
Open sourceSelf-hostedTopic-threaded chat that keeps busy channels readable.
Zulip organizes every message into a topic within a channel, which keeps fast-moving conversations far more readable than a flat Slack-style feed — worth a serious look if your team has ever lost a conversation thread in a busy channel.
- Topic-based threading within every channel
- Full-text search across all history
- Markdown formatting and code-block support
- Self-hosted or a hosted cloud plan
Licensing and pricing models change over time — confirm current terms on each project's own site before making a procurement or compliance decision.
Frequently asked questions
What's the closest free alternative to Slack?
Rocket.Chat looks and feels most like Slack out of the box. Mattermost is the stronger pick if your team is developer-heavy and wants tight tool integrations; Zulip is worth it specifically for its topic-threading if busy channels have been a problem.
Do these tools keep full message history like Slack's paid plans?
Yes — that's one of the main reasons teams self-host chat in the first place. There's no 90-day cutoff; history is retained as long as your server keeps it.
Can I use these tools on mobile?
All three have mobile apps (iOS and Android) alongside desktop and web clients, so the switch from Slack doesn't mean losing mobile access.
More free alternatives
Not sure which way to go?
A free Growth Audit can help you weigh self-hosting against the tool you already pay for.