Pidgin - Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.

Demonsaw - Demonsaw is the next leap in the evolution of a free Internet, and the debut of social cryptography.

Trillian - Trillian is a decentralized and federated instant messaging platform that lets your whole company send private and group messages, keep tabs on what co-workers are doing, share files, and much more.

Jitsi - Open-source video calling and chat platform.

Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.

i2pd (I2P Daemon) - i2pd (I2P Daemon) is a full-featured C++ implementation of I2P client