What about Tox ? It is distributed, encrypted by default & zero setup. It also does not do any of the privacy invading crap like Whatsapp & co do and is fully open source. As for audio and video chat - it works fine on desktop (tried Linux-Linux, but it should work just as fine with Windows & MacOS) and it can automatically traverse NAT, so no manual port forwarding is needed. There are also mobile clients - Cyanide for Sailfish OS and a client for Android. But I'm not sure how far are the mobile clients with audio & video chat support.