Otherhome

Use Otherhome app for communicating with Otherhome friends and colleagues without surrendering your data to large corporations.
To get started with the app you need an invite to a Otherhome service, or run your own. The app will not work unless you have an invite to join a Otherhome service.
Otherhome lets you use services provided by people you trust. This means that Otherhome strives to protect your privacy and secure messages.
Both the app and service are 100% free and open-source software.