https://getconfide.com/

Signal – https://theintercept.com/2015/03/02/signal-iphones-encrypted-messaging-app-now-supports-text/

The reason staffers chose Confide over other secure messaging apps, like Signal, is that Confide erases messages as soon as they’re read.

Other secure messengers, like Signal, do not wipe read messages — meaning they could be intercepted if someone gains access to a phone where the messages have not been explicitly deleted.