Open Source Alternatives

Alternatives to Slack

Team messaging and collaboration platform.

3 drop-in replacements1 building block

Slack is a trademark of its respective owner.

Updated Apr 2026

Quick Compare

	Zulip	Rocket.Chat	Mattermost
Score	16	16	16
Overlap	78%	82%	85%
Migration	moderate	moderate	moderate
License	Apache License 2.0	MIT License	MIT + AGPL
Best for	Teams with DevOps	Teams with DevOps	Small teams

Drop-in Replacements

Ranked by Discovery Score

Zulip

1678% coverage

Team chat with threading

Zulip fixes chat overload with threading that actually works. Every message belongs to a topic within a stream (channel).

25.0k ★+41/wkPythonApache License 2.0

Rocket.Chat

1682% coverage

Open source Slack/Teams alternative

Rocket.Chat is a self-hosted messaging platform where you control the data and no vendor decides to change pricing on you. battle-tested, used by government agencies and enterprises that can't put conversations on someone else's cloud.

45.1k ★+61/wkTypeScriptMIT License

Mattermost

1685% coverage

Open source secure collaboration platform

Channels, threads, file sharing, integrations, video calls. It looks and works like Slack because that's exactly what it's replacing.

36.1k ★+77/wkTypeScriptMIT + AGPL

Building Blocks

Slack is a platform — it bundles multiple capabilities into one subscription. These tools each cover one piece. Teams often assemble 2–3 of them instead of paying for the full suite.