Riot.im!

All-in-one voice and text chat for gamers that’s free, secure, and works on both your desktop and phone. Stop paying for TeamSpeak servers and hassling with Skype.

WhatsApp Messenger is a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for iPhone, BlackBerry, Android, Windows Phone and Nokia and yes, those phones can all message each other! Because WhatsApp Messenger uses the same internet data plan that you use for email and web browsing, there is no cost to message and stay in touch with your friends.

Mumble was the first and is the most successful and wide spread free and open source software for VoIP. It was the first VoIP software to provide low-latency audio suitable for gaming, and at the same time was a pioneer in high audio quality at the same time.

Diaspora is a federated social networking service, designed to be a more privacy-aware alternative to Facebook . Share what you want, with whom you want.

With Viber, everyone in the world can connect. Freely. More than 460 million Viber users text, make HD-quality phone and video calls, and send photo and video messages worldwide over WiFi or 3G - for free. Viber Out can be used to make calls to non-Viber landlines and mobile numbers at low rates. Viber is available for many smartphones and platforms.

Facebook Messenger is a faster way to message. Reach friends right on their phones, get and send messages fast, message everyone at once and more.