Free download HERE
Very easy to install, configure.
Don't think it would be very hard to run it inside xoops.
I run it externel so ppl can keep browsing web site and wait for someone to come in the chat room.
I did set up a block letting ppl know how many are in chat room.
This block is on the left side at the top of every page, is also a link to the chat room which opens up in a new popup window.