Sorry It's Over - Breakup as a service
BURN.link - Send secure, encrypted, self-destructing messages
Cocoon - Cocoon is a special app for your most special relationships, designed to keep you close no matter where you happen to be.
sup3rS3cretMes5age - A safe, simple tool for one-time (self-destructing) messages
ExBox - Cold storage for anything that reminds you of your ex
1ty.me - If you need to send a password or some other form of simple but sensitive information to someone...