Although I only live with 4 others, wife, son & 2 cats, in a small 5 room apartment most evenings we are in different rooms, or in the summer 3 different floors, wearing headphones chilling to our own choices in music & tv. As I think it’s uncouth to yell out of the window or across the apartment to get someone’s attention I setup a Raspberry Pi Model B as an XMPP server running MUC. As it’s only for 3 people, unless we have visitors, I chose to run Prosody, it’s pretty lightweight, easy to setup, the stable version is in the raspbian repos & i’ve used it before. I’ve also used and run ejabberd, openfire, tigase, jabberd,… but IMHO they are heavier on resources and a bit harder to setup, and are overkill for my needs and anyway I like lua.

Full article here:
Setting up Prosody on the Raspberry Pi for house/apartment/secret club house-wide chatroom (Executing Gummiworms)
NOTE: The author appears to have taken down the above article, but there is a cached version at the Wayback Machine.
Related articles:
Using the prosody xmpp/chat server (Debian Administration)
Installing Prosody XMPP Server on Ubuntu 12.04 (Precise Pangolin) (Linode Library)