Zulip Is a Free Team Chat Client From Dropbox That You Can Host Yourself
Over the past couple of years, services like Hipchat and Slack have become popular ways for companies and teams to manage their communications. Zulip is a completely free and open source Dropbox alternative with many features.
The service requires someone on your team to host their own server, which currently only runs on Ubuntu. However, if you can get past that hurdle, Zulip has clients for Mac, Windows, Android, and iOS. You can add integration with external services, share files, customize notifications, and more.
Zulip via Android Police