Meebo, the most popular web based IM service is powering the channel chats in Joost. This is different from th Instant Messaging chat in Joost, with IM chat you can connect to Gtalk/Jabber based services. With Meebo you can connect with other users watching the same channel and interact with them.
I don’t see any option to login to Meebo and chat with Yahoo or MSN as others are reporting. May be full integration is not yet implemented or it is only channel chat not messenger buddy chat.
Sadly, for some reason, Joost doesn’t work on my PC.