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Mattermost vs Fluxer: catalog facts
Mattermost	Fluxer
Freemium The desktop client is free and open source. The Mattermost server has a free self-hosted…	Free Free and open source under the AGPL-3.0.
Windows, macOS, Linux	Linux, Android, Web, Self-hosted
The server is self-hosted, so message data never leaves your infrastructure Server dropdown lets one client connect to several Mattermost instances	Text, voice, video and screen sharing in one app Can be self-hosted with data kept on your server
Needs a Mattermost server, which is real infrastructure to run Electron, so memory use is high for a chat client	Desktop app support for self-hosted servers is still coming Younger and smaller than established chat platforms
Downloadable app	Downloadable app, Web application, Self-hosted, Hosted service
Open source	Open source
License: Apache-2.0	License: AGPL-3.0-or-later
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 October 1, 2026

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