A popular project type among open source developers is finding new uses for old hardware. There are several projects to turn an old PC into a firewall appliance, FreeNAS turns an old (or not so old) computer into a Network Attached Storage (NAS) device. With many households having more than one computer now, keeping files on each computer is wasteful of storage space and frustrating because the file you need is always on "the other computer". This is even more true in a business environment. Keeping shared files on one computer and sharing them over the network makes sense, but leaving a powerful, and power hungry, desktop computer turned on just to make some files available is hardly green, or economic sense.
FreeNAS turns an old, low powered computer into a network storage solution. Plug in a decent sized USB hard drive and you can keep all your media (or business) files in one place. FreeNAS supports most network file access protocols: CIFS (Windows file sharing, formerly SMB), FTP, NFS, TFTP, Rsync and Unison to mention a few. The support for rsync and Unison means you can also use your NAS as a backup device, especially useful for a laptop where you need local copies for when you take the laptop out but need copies back at base in case it gets lost, dropped or stolen and you don't bring it back.
FreeNAS can run from a CD, USB stick or be installed to a hard drive. When run from CD it can store its settings on a USB or floppy drive, making it even more secure because the programs cannot be corrupted by a hacker. Most of the time, you just leave a NAS box alone, it needs no keyboard or monitor. If you do need to administer it, FreeNAS has a web interface that you can access from any other computer on your network. FreeNAS has several other useful features, such as support for RAID and encryption, both giving improved security to your data in different ways and monitoring of your disks' health with email alerts.
An excellent use of an otherwise redundant computer. FreeNAS improves your efficiency and security while doing your bit for the environment.