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Zulip vs Flock: catalog facts
Zulip	Flock
Freemium The server and clients are free and open source and can be self-hosted at no cost. Zulip…	Freemium Sign-up is self-serve; check the site for current plans.
Windows, macOS, Linux, Android	Web
Topic-based threading inside channels, which makes catching up genuinely practical Self-hostable, or hosted, with free plans for open-source communities	Channels for organising team discussion Built-in voice and video calls with screen sharing
The topic model takes getting used to and needs team discipline to work The desktop client shares most of its code with the web app, so it inherits its quirks	Proprietary hosted service; data lives on the vendor's servers Aimed at organisations rather than personal use
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 24, 2026

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