This is probably sooo baked, let's see.
Our office has a stereo system; each of us stores our mp3 tunes on our laptop. Laptops all connect via Wifi/LAN.
At the moment we pass a mini-jack across the table so we can take it in turns to play music through the speakers. We could buy a 7-input stereo
mixer, but that would take up too much room; this wouldn't solve the problem of the 'DJ' not concentrating on their setlist due to silly things like phonecalls, coding, etc.
A 'network playlist' program would solve our problem. It would run on one computer, which would remain connected to the stereo. The other machines would be able to add tracks to the network playlist (from their own hard-drives), and hit an 'argh' button to vote out unpopular tracks.