New life for old PCs using pre-configured Linux appliances

OpenWRT runs on loads of "obsolete" hardware, MIPS being highly popular. Recover any of the below (second hand, online market, forums) and you got yourself an efficient home server, preferably with USB for storage. Gives you VPN, dropbox without handing data to third parties, a real homepage, 24/7 torrent etc. for literally less than a dozen W. Brings back its price in electricity bill within a year, besides being a good 'toy'.

http://oldwiki.openwrt.org/TableOfHardware.html

Old laptops are more energy efficient than old desktops. I use a few 10+ year old machines for various dedicated purposes. While most have no internal batteries, I plug them into a small $25 UPS and get the same brief power outage resilience that an internal battery would provide.

Sheeva plug (and similar Plug computers):

http://en.wikipedia.org/wiki/Plug_computer

Fit PC

http://www.fit-pc.com/