There are already countless chatting software (such as WhatsApp, Skype, Discord, Facebook Messenger), but almost all of them are non-free software based on central servers, and their security and privacy are not guaranteed (any chat history of you will be sold to various companies). Many of them claim to encrypt communication content, even with end-to-end encryption, but when a platform is proprietary, there is simply no way for others to verify that it is as secure and private as it promises to be. Of course, there are some really safe and reliable ones, but they are frequently blocked by governments of various countries and cannot continue (such as Signal, Telegram).

TeamTalk is a free and open-source multi-user conferencing system for Windows, Mac, Linux and mobile platforms, developed by Bjoern D. Rasmussen from Denmark. It allows user to perform real-time voice and video communication through Internet. For voice encoding, it uses the Opus and Speex audio codecs; for video streaming, it uses the WebM video codec.

TeamSpeak is a very excellent free and cross-platform professional team VoIP (Voice over Internet Phone) communication application specially designed for online gamers around the world. It was developed by TeamSpeak Systems from Germany in 1999, and has become one of the most popular and renowned voice communication platforms for online games in the world.

Jitsi (AKA: Jitsi Desktop, formerly called SIP Communicator) is a powerful, scalable, secure (using the SIP/RTP/SRTP/ZRTP encryption algorithms), high-quality and community-driven VoIP/video conferencing/instant messaging application from France, written in Java. It's free, open-source, cross-platform (across Windows, Linux, Mac OS X desktop platfroms and Andrjoid, iOS mobile devices), multi-protocol and multi-user on use and allows to be made secondary development.