Chadder - Encrypted messaging app
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
GrapheneOS - GrapheneOS is an open source privacy and security focused mobile OS with Android app compatibility.
Keybase Chat - End-to-end encrypted chat built into Keybase
Earlynote - A time-travelling messaging app
Crypho - End-to-end-encrypted messaging and file sharing