Dr Mario

Dr Mario is an unofficial clone of the popular game by Nintendo. (Please don't sue!) The author only asked for $1 for his game, probably because he recognized it wasn't exactly his original idea. It doesn't actually have any images of the famous plumber in the game, but it plays pretty much like the original, which is impressive given the tiny size of the .EXE file. There are no options to set, you just begin the game and play for as long as you can. I'm pretty sure this is using a modified text-mode, where the default character set has been edited, which is also impressive in its own way.