Spent the morning working on my old PIII web server, Updated it. Added a web application or two. Always learning new things with it. Can not believe how much I have done with it. It is basically a lamp server, but we also use it to start ipxeboot linux operating system installs, and as a media/game server. It is sort of our own private cloud. It also runs several virtual websites. http://www.instructables.com/id/Uses-for-your-own-private-cloud/)
Home made router with a PII class machine that uses compact flash for the drive and a bsd variant for the os.
The old Pogoplug converted into a local web server running arch linux. The 486 laptop runs a floppy based Pitus linux to communicate with the pogoplug.
The old NSLU2 running debian as a sort of jack of all trades server,
The linux terminal server running a Debian flavor linux for use in the classroom. Internet filtering software is also installed such as dansguardian. tinyproxy, and etc.. We originally started with floppy based 486 systems and eventually went to the pxebootable Compaq T30s. No operating system software is on the thin clients. The server does all the heavy lifting. http://www.instructables.com/id/Another-almost-free-computers-thin-client-set-up/
My desktop running debian linux.
My mini RPi desktop with a dvd player as the monitor.
Mythtv - computerized PVR
Open source rocks.