Mattermost is an open-source communication & social tool — Self-hosted team messaging and collaboration platform, AGPL-licensed; an alternative to Slack.

Is Mattermost free and open source?

Yes. Mattermost is free and open source, released under the Apache-2.0 license. You can view and contribute to the source at https://github.com/mattermost/mattermost.

What are open-source alternatives to Mattermost?

Other open-source communication & social tools on OSSDrop include Mastodon, Discourse, Rocket.Chat, Chatwoot.

Mattermost

Curated

Self-hosted team messaging and collaboration platform, AGPL-licensed; an alternative to Slack.

Visit mattermost.com Source

Communication & Social·Apache-2.0·38.6k stars·v11.9.0·added 2026-07-30

Curated listing — added by OSSDrop, not the maker.

Frequently asked

What is Mattermost?
Mattermost is an open-source communication & social tool — Self-hosted team messaging and collaboration platform, AGPL-licensed; an alternative to Slack.
Is Mattermost free and open source?
Yes. Mattermost is free and open source, released under the Apache-2.0 license. You can view and contribute to the source at https://github.com/mattermost/mattermost.
What are open-source alternatives to Mattermost?
Other open-source communication & social tools on OSSDrop include Mastodon, Discourse, Rocket.Chat, Chatwoot.

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