Comment by volitek

Tox (http://tox.im)

Secure, encrypted, instant messaging, voice, and video, over a distributed network, aiming to be easy enough to use to completely replace Skype.

The core is a library written in C, and there are several different clients in different languages, help on any of them or the core would be great.

https://github.com/naxuroqa/Venom (Vala/GTK+ cross platform client)

https://github.com/stal888/Poison (Objective C OS X client)

https://github.com/Astonex/Antox (Android)

https://github.com/Jman012/Toxicity (iOS)