Linux

Linux as an OS is just so much better about getting good performance out of the hardware, and keeping itself out of the way. I've converted a lot of people to Linux over the year in an effort to get better performance on older systems. They couldn't afford to buy a new computer, and usually just wanted to be able to check email and go on the web. Slap Ubuntu on and they were always shocked how much better everything ran, but was still easy to use.