A piece of encryption software for mobile instant messaging that is relatively easy to install and use is Threema https://threema.ch/en/. It appears to be quite popular among 30C3 attendees this year. I was also able to convince about 20 of my non-geek friends to use it instead of WhatsApp.

It doesn't support group chat on Android yet (on iOS it does), but it's under development.

The security section on the FAQ page might be interesting to HN readers: https://threema.ch/en/faq.html

(I'm not affiliated with Threema)