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Mattermost vs Slack: catalog facts
Mattermost	Slack
Freemium The desktop client is free and open source. The Mattermost server has a free self-hosted…	Freemium Free plan available, with paid plans for more features.
Windows, macOS, Linux	Windows, macOS, Linux, Android, iOS, Web
The server is self-hosted, so message data never leaves your infrastructure Server dropdown lets one client connect to several Mattermost instances	Channels keep team conversations organized Large range of app integrations
Needs a Mattermost server, which is real infrastructure to run Electron, so memory use is high for a chat client	Closed source hosted service Many features and AI tools sit behind paid plans
Downloadable app	Downloadable app, Web application, Hosted service
Open source	Closed source
License: Apache-2.0	License not stated
Account needed	Account needed
Needs internet	Needs internet
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked September 23, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.