From Zemerick Software:
Chat Controller gives parents the power they need to take control of their children's instant messaging. Chat Controller will block all popular instant messengers, such as AOL Instant Messenger, Windows Live Messenger, Yahoo! Messenger, and many more. Chat Controller allows for creating "rules" for when chatting is not allowed per user and per instant messenger. Easy to use and effective.
What's new in this version:
Version 2.0 added compatibility for Windows 7 and support for more instant messengers.