I have an old server at home that I wanted to use as a NAS (2TB) device. For basic home NAS use I have found FreeNAS to be satisfactory. It is limited, but has some really nice features such as support for Dynamic DNS which periodically updates DNS servers with the NAS’ IP address, a great feature for small home office users who use normal residential internet service which usually has a dynamic IP address…
If you have not heard of it, FreeNAS is a free NAS (Network-Attached Storage) server, supporting: CIFS (samba), FTP, NFS, AFP, RSYNC, iSCSI protocols, S.M.A.R.T., local user authentication, Software RAID (0,1,5) with a Full WEB configuration interface. FreeNAS takes less than 32MB once installed on Compact Flash, hard drive or USB key. The minimal FreeBSD distribution, Web interface, PHP scripts and documentation are based on M0n0wall. (Which is another solid solution…)

Trove info

Underlying operating system: FreeBSD 6.4
Hardware requirements: 128MB of RAM minimum
Language: Mostly PHP
Licence: Modified BSD