Delta Chat is a free open source encrypted messaging system that works through email (so it is federated too). You can follow at:
There are apps for Android, iPhone/iPad, Linux, Mac and Windows. More info at https://delta.chat
(You can also message people on conventional email accounts unencrypted.)
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!