Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
sup3rS3cretMes5age - A safe, simple tool for one-time (self-destructing) messages
Sorry It's Over - Breakup as a service
BURN.link - Send secure, encrypted, self-destructing messages
Geneva - An all-in-one communication app for groups & communities
Boop - A scriptable scratchpad for developers. Free & open source!