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. By selecting the "Multipanel" view, you should be able to log into IRC in the sidebar, but keep your main browser still usable.