Commander Keen 2000
This was the first ever Commander Keen fangame, finished by A.R. on November 24, 1998. Although Netkeen was released a year earlier, CK2000 was the first complete fan-made Keen game. Despite this, it is a whole lot better than a lot of ones made later. Most of the graphics are ripped, but there's some new ones too, such as the giant chicken boss near the end. A Hungarian translation by Szemigi was released in 2010.
The game doesn't scroll and has very buggy movement; it is of a reasonable difficulty and set the standards for other fangames.