FreeNAS

http://www.freenas.org/

FreeNAS is an operating system that can be installed on virtually any hardware platform to share data over a network. FreeNAS is the simplest way to create a centralized and easily accessible place for your data. Use FreeNAS with ZFS to protect, store, backup, all of your data. FreeNAS is used everywhere, for the home, small business, and the enterprise.