Abandonware is software that is officially not supported by companies anymore. This basically means that it's now a light grey area concerning downloading it for free (definitely the older stuff, but a case could be made that Windows XP SP 0/1 is abandonware...). So you can visit this site:
and download Windows 1.0! I'm currently trying to get it up in a virtual machine =] and I'll post back, maybe with screenshots.
It's not just hardcore stuff for nerds, though; there's office suites, graphics, design, and games. Ever wanted to play SimCity 2000? Ever wanted to play The Incredible Machine 2 (TIM 1 runs on a 286 @ 10 MHZ with 1 MB of RAM! Yes, I do have an IBM PC AT-286, and am proud of it =])? You can get them here, too.