Zulip is a free/open source group chat server. It has a web interface and it’s basically a very very very good competitor to Slack (which I’ve advocated for use in multiple companies). Multi-user/group chat makes collaboration easier and it avoids the dreaded 20+ email chains that happen for important company topics.
Zulip has clients for Mac OS X, Windows, Android and iPhone.
The differentiating factor, what makes it different from Slack and HipChat, is that you can organize chats around topics. So for example, if you’re discussing a section of the FAQ or Help documents, you can organize a topic chat for that section. Another example is if there’s a major server issue that needs to be fixed; you only need 3 people on that topic.
What I really enjoy is the API and integrations. Because Zulip is free/open source, the full stack from Zulip to the integrations can be free/open source. This gives you a lot of power because if Zulip is missing something necessary for your integration to work, you can just jump into the code and add it.
This is the most promising competitor and I’ll be advocating Zulip from now on instead of Slack. Thanks to Dropbox for developing Zulip and choosing to make it free/open source.