When Discourse was submitted to HN, this immediately came to mind, though I couldn't remember its name. It was a breath of fresh air in terms of approach and design style. It would be awesome to see chat-forum hybrids like this become popular, because I've wondered what could be done with a more evolved IRC. I only regret it's not in a language I operate in, and I'm not sure how easy it'd be to customise to add features.

A little tip - hit Ctrl+Enter to post your message.

Here's the relevant discussion thread (thanks davidcollantes), which got lots of comments and upvotes:

http://news.ycombinator.com/item?id=4499845

There's also an open-source release of it, but it seems not to have been updated in months:

https://github.com/cheshirecats/CuriousWall

(Also, is there a bug with scrolling on Chrome? No matter whether I scroll up or down, my mousewheel sends me down the page.)