We have set up an IRC channel, #apache-isis, on freenode.net.
There are lots of good IRC clients around, but if you don't habitually use IRC, then you might want to use the webchat client that freenode.net provide
Accessing as a web page
Follow this link: http://webchat.freenode.net/?channels=apache-isis&uio=d4, enter a nickname, and you're in:
Accessing in Firefox sidebar
If you use Firefox then here's a way to keep the IRC session open. First, install the All-in-one sidebar. Then, by selecting the "Multipanel" view (a squat, blue cross icon) you should be able to log into IRC in the sidebar, but keep your main browser still usable.