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.

Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems

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.

MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.

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

Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).