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