The Linutop is a tiny Linux computer that you stick onto the back of your flat screen monitor (and hook it to the monitor, obviously), plug in, and go. It makes no noise, produces very little heat, uses hardly any electricity (eight watts) and seems to be reasonably powered. It cost about 300 bucks.
There are things it won’t do. The system is solid state, which means it is totally secure but upgrading would not be done in the usual way. I believe this computer is what you want to use if you are not storing data or if all your data is stored on line.
But for public computers in internet cafes or hotels, as your second computer in your home network, etc. this may be just the thing.