Open source.

Zulip is 100% open source software, built by a vibrant community of hundreds of developers from all around the world. With 120,000 words of developer documentation, a high quality code base, and a welcoming community, it’s easy to extend or tweak Zulip.

Zulip has a significantly larger and more active development community than other modern open source group chat solutions like Mattermost, Rocket.Chat, and matrix.org.

Install Zulip 3.0 or read the Zulip 3.0 release announcement.