I was trawling around The Home of the Underdogs, my favourite Abandonware site, when I happened upon this rather wonderful bit of Freeware, DoomRL.
It's a remake of Doom, but as a Rogue-like ASCII based hack-n-slash RPG; hence the name, DoomRL. It may sound like an odd concept, but once you learn all the commands and get to grips with it, you'll love it. DoomRL has the same kind of appeal as hack-n-slash classics like Nethack and ZangbandTK. They're not going to graphically set your world alight, but they're lots of fun if you can see past the archaic interface. A definite cult classic in the making, and only a 1MB zipped download.