CoSketch - CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images. No registration or plugins required.

Empathy - Apps/Empathy - GNOME Wiki!

Conceptboard - Instant Whiteboards for Teams & Projects

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.

Twiddla - Mark up websites, graphics, and photos, or start brainstorming on a blank canvas.

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.