Commander Keen 0: Part 1
Commander Keen 0: Part 1 is a Keen 1 mod by ElecDude33. It has no storyline, but a text file included with one version of the mod stated that the story was "Keen goes to a place."
Many of the enemies look like squares or blocks. The graphics contain various superfluous crosses, somewhat intended as a parody of incomprehensible religious symbolism in anime and video games. The map level is very basic, with the levels all in a line. This was supposed to be a placeholder map until a more complex one was created, but it remained in the final version, although "proper" map levels had been tried a few times and given up on beforehand.
A special edition was created for April Fools Day. In this version, the colours of the graphics were inverted and the exits to most levels were placed very near the beginning. In addition, parts of many levels were made inaccessible. In this special edition, the story text states that "everything goes weird". (?)
It would be fair to call the release history of the mod confusing. ElecDude33 has lost access to almost all old data that could help clear up some of the confusion, but were they to find it, some sort of rudimentary "making of" would be a possibility.
A fairly early and amateurish mod from a modder whose efforts to produce more polished later mods have, thus far, failed to result in any finished product. Which is not to say that one won't eventually happen, nor to say that it will.
Note About Text
With lack of knowledge regarding patching, text edits in Commander Keen 0: Part 1 were done by hex editing of the EXE file rather than patching. As there are potential legal issues with modifying the executable and a patch is the more accepted way to change text in a mod, there have been occasional plans to release an updated version using patching instead, but so far it hasn't been done.
Some levels show repeating patterns in a "more difficult retread of an earlier level"-type style. One of these repeated levels still shows possibly recognisable elements of the first level of the original Marooned on Mars.
Spoiler Warning! This shows the whole levels.