All three unRAID editions boot from a USB flash disk and run entirely in as little as 512MB of memory. The free, basic version supports up to three data drives, the $69 Plus edition raises support to six drives, and $119 buys the Pro edition that can support up to 22 drives (20 data plus one each parity and data) and use Active Directory for authentication. Lime Technologies even sells 15 bay NAS systems, using Celeron or Core 2 processors and a "Best of Newegg" parts list including SATA hot swap trays for $1200-$1400. An active user community supplies scripts and add-ons for things like running a web server on the Linux based unRAID system or recalculating parity on a scheduled basis.
unRAID will become even more interesting when Line Technologies adds P&Q double parity and the ability to create multiple unRAIDs in a single appliance down the road. While I wouldn't use unRAID in a corporate environment or recommend they add iSCSI support, it seems to be a clever solution to the problem of storing large media files.