Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Chadder - Encrypted messaging app
WhatsApp Desktop - WhatsApp, now on your desktop
GrapheneOS - GrapheneOS is an open source privacy and security focused mobile OS with Android app compatibility.
Wafer Messenger - Endless Creativity, Limitless Reach.
Earlynote - A time-travelling messaging app