I recently found out about this software called 'Whisper' which basically has peer to peer encryption, fully open source and has iOS and Android support. I think it's something good since apparently microsoft can log all of your skype conversations etc, and I'm always looking for open source alternatives lately.

If you go here: Whisper beta you can sign up for the desktop version, there is a waiting list but eventually you'll get access.

EDIT: As pointed out by Meph1stoo, https://tox.chat/ is actually much better and has more platform support.