Slack Alternatives for Team Communication

Zulip

25,87810,210

Zulip is an open-source team chat application, and a self-hosted alternative to Slack. Its distinguishing feature is topic-based threading: every message in a channel belongs to a named topic, so conversations stay separable and catch-up reading is fast even in busy channels. It offers full-text search, hundreds of integrations, interactive bots, and native mobile and desktop apps.

Mattermost

31,1167,467

An open source platform for secure collaboration across the software development lifecycle, enabling teams to communicate, coordinate, and manage projects efficiently.