The OS I'm using atm runs in RAM. It will run with 256KB. It lives on a USB drive.
I plug it in, do my stuff and then unplug it. There is nothing on my hard drive.

It's Linux of course.

Hopefully when my package arrives from the UK there will be a mini PC I bought.
All that pile of crap in the picture will go. The mini PC is about the size of a hard drive.

It uses 7Watts of electricity and for day to day stuff it's as fast as the Intel i5 I've got sitting in the box beside me.
I built the large silver PC you may have seen in other pictures to play a particular game on; Unreal Tournament 3. The game is unfortunately tied into Windows XP and thus not really playable these days.

There are workarounds which I will investigate another day. Atm it's just get the net running reliably.