The company's main product is the Sonos Multi-Room Music System. The Sonos(R) Multi-Room Music System is a modular set of digital appliances that works with end-user supplied speakers to form a zoned audio system in which different zones may play the same or different Audio. The Sonos Multi-Room Music System creates multi-room audio hi-fi in which different zones may play the same or different songs simultaneously throughout the house. The company tagline is "All the music you want. All over your house. All from the palm of your hand." There are two main appliances in the Sonos Multi-Room Music System: ZonePlayers and Controllers. ZonePlayers may connect directly to speakers, or to an amplifier, and take the place of a traditional hifi setup. The system is controlled by the Sonos Controller, a wireless handheld Remote Control equipped with a color LCD screen, scroll wheel and buttons that control music streaming and zone selection. Software is also available for iPhone and iPod touch, Mac, Windows computers to control the system.
Mar'2006: Fred Wilson plugs it and includes pricing info. My biggest concern is the cost. The system I got, the Introductory Bundle, costs $1200 from Sonos. You may be able to get it for less somewhere else. And if you need more than two zones, each Zone Player is $500 and each Wireless Controller is $400.
http://en.wikipedia.org/wiki/Firefly_Media_Server an open-source media server (or daemon) for the Roku Sound Bridge and ITunes. It serves media files using Roku Server Protocol (RSP) and Digital Audio Access Protocol (DAAP).