FreeNAS will take any computer with some storage attached (say, a few hard drives) and will allow them to be addressable devices on a network. The ISO is only 46 megs in size, the OS installed on a hard drive takes up a mere 32megabytes!
Once installed (takes about 3 minutes), you can do a basic setup with it’s text-based interface by setting up it’s IP address, subnet mask and gateway. Once that’s completed, you can address the server via the web interface which is simple & robust.
From their About page:
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.
One of my older servers now runs FreeNAS with a 250gig internal drive, and (2) 250 gig external drives, seamlessly detected by FreeNAS and made available now as NFS shares to my other computers or laptop from outside the network via encrypted tunnel (SSHFS). It is also capable of using wireless interfaces! It also integrates with Active Directory and LDAP servers and gives live feeds on bandwidth & CPU usage. It also supports Rsync, SNMP messaging and SSH tunneling.
Here’s a great review on the benefits of FreeNAS from (2) years ago, that is very well-written. In fact, much more functionality has been added since this review, such as drive-encryption and iSCSI, but the review is worth reading nonetheless.