Developer: id Software
Release Date: December 14, 1990
Source Code Release Date: Not formally released

Not only is this literally id Software's first game, but they didn't even go by id Software yet, they went by the name Ideas from the Deep. Commander Keen in Invasion of the Vorticons is a shareware side scroller with EGA graphics that predated sound cards. The first game in the series consisted of three episodes, and the Commander Genius source port went so far as to reverse engineer the PC speaker sound effects the game relied upon.

Note that most digital retailers market someting called the Commander Keen Complete Pack which contains the first two games' content but not the Keen Dreams spinoff or the final episode Aliens Ate My Babysitter due to the surprisingly complicated publication history of the series. Commander Genius has incomplete support for Keen Dreams, but fully supports Aliens Ate My Babysitter, should you be able to find it somewhere.

  Buy Commander Keen in Invasion of the Vorticons on GOG.com