Who here remembers the side-scrolling platformer, Crystal Caves? This was a computer game from around 1991 produced by ID but published by Apogee. It's quite similar to Commander Keen.
You played this guy named Milo Steamwitz who went through levels collecting gems and firing a gun at enemies. The levels could be taken in any order. It was part of a trilogy. The first episode was called "Trouble with Twibbles" (a parody of the Star Trek ep "Trouble with Tribbles") - you could get that as shareware. The other two episodes required you to pony up money.
I used to play this in school. On Fridays in my computer classes, we were allowed to play various shareware games and this was one of them. It could get hairy in some places, especially when you had to change the gravity controls.













