Privacy is a precious thing, but it can be difficult to be sure of these days. For those who are concerned about keeping the contents of their messages completely safe from prying eyes, there's PQChat. It encrypts messages, and it does so in such a way that each message is encrypted differently. It uses the McEliece Cryptosystem – a system that has never been broken.
There are lots of features to be found in this app including group chat, presence updates so you can see if your mates are online, message flagging to keep the important ones easily accessible, a vault for storing your vital personal info like credit card details, and more. You can set a timer for messages and when that timer is up the message is scrubbed.
To take advantage of the app's features it has to be used at both ends of a conversation so if you are interested in it, you'll need to ask other people to download it too. At present PQChat is an iOS-only app, but an Android version is expected soon.