For BarCamp, we are using a web based chat program called Pibb. It's made by the good folks at JanRain, who have done some amazing work on OpenID. Using this identity backbone, they also created a fun site called Jyte for asserting and voting on claims. But the thing I'm really stoked about how they integrated IRC through a bot. For years we've begged for a simple web based client for IRC, partially because nobody knows what IRC stands for or what client to download or how to set them up.
No, I didn't say IRC 2.0.