Killer-tool! We have built some integrations to it to make our communication asynchronous (humans vs. humans, devs vs. servers, etc.), and got plans for even more. I know people been doing this for looong for IRC, but I find HipChat more usable for non-hackers (the biz folks "get it") and it's more tweakable (visually via HTML-formatting). Lovely.

Added it.

For every tool I have on the list there are probably equally 3 good tools I don't have listed yet.