Here's a couple more
Doom Episode 1 tributes that work with
Freedoom:
Phobos Revisited
The aim of the author was to create a "same but different" kind of feeling, following the original levels quite closely yet introducing something new at every turn.
Phobos Revisited was designed to run in the original game as well as with source ports, and it won the
Cacowards award in 2004. Screenshots can be viewed
here at the team's website.
Phobos Outpost/Planet Phobos
Another interesting work, this one deviates a lot more from the original - for example, the first level is nothing like
Doom's E1M1 - however later on similar details and areas become more frequent. The levels here are supposed to represent a single, coherent installation (the eponymous outpost), and at the end of each level the starting area of the next one can briefly be seen. Difficulty is a bit higher than in other similar works, or in the first episode of the original game for that matter, but clever design makes them interesting to play. For some reason, the author renamed the episode to
Planet Phobos at some point, although no content was apparently changed.
The same author also released an Episode 2 replacement,
The Base of Evil (which was also renamed to
Planet Hell later), however it doesn't seem to work with
Freedoom for now because of a missing textures issue.