MostlyMatter
MostlyMatter is an open-source platform for team communication, based on Mattermost — a fork maintained by Framasoft, a French non-profit organization. Create public and private channels, send direct messages, start calls with screen sharing, and organize people in teams. The privacy-first alternative to Slack and Microsoft Teams — GDPR-compliant on servers in Germany.
MostlyMatter started as a practical response to Mattermost’s licensing policy. Mattermost’s free edition (Team Edition) caps the number of users — with version 11, Mattermost lowered that limit to 250 users (down from 1,000). Teams that need more accounts have to move to a paid license.
Because Mattermost is open source, Framasoft — a French non-profit that relies heavily on Mattermost for its own “Framateam” service — started the MostlyMatter fork in 2024. A small patch (limitless.patch) raises the user and message limits so high that they effectively no longer apply. Aside from that, MostlyMatter is functionally identical to Mattermost and tracks its releases (currently Mattermost 11); the source code is openly available under the Apache 2.0 license.
So MostlyMatter is effectively Mattermost without the free edition’s user cap: the full feature set, but no artificial limit on team size. At server.camp it runs as a fully managed service — with backups, updates, and the call servers already set up for you.
Our Getting started with MostlyMatter walks you through your first sign-in, structuring channels, inviting users, and using calls.
Find answers to common questions on the MostlyMatter product page. Still have questions? Reach out any time.