Openfiler is an enterprise-grade, Linux-based networked attached server (NAS) cum storage area network (SAN) distro. It is the only Open Source and free NAS/SAN solution that we know of.

FreeNAS is a m0n0Wall-based, Network Attached Storage (NAS) server designed mostly for embedded systems, but may be installed on generic PCs or USB key. It is developed by Olivier Cochard-Labbé and released under the BSD license.