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.
Warmspace - Tech-powered conversations that transform relationships in work and life.
LimeChat - LimeChat is an IRC client for Windows, Mac OS X and iOS. Features
oorja - Your Dedicated Meeting Spaces Online — no installations
Adium - Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more.
ClearChat - If you're hosting a public video chat then it can attract unwanted attention from troublemakers.