It tries to recreate the shadow system from games like Duke Nukem 3D and Shadow Warrior and apply it to Doom.
This is more of a proof-of-concept than anything and you shouldn't really use it (unless you're weird like me and likes playing on an outdated source port).
If you really want some sprite shadows in your Doom you should just use Nash's mod.
Welp, here's the download link. (Does NOT work on Zandronum)
Note: For the shadows to correctly appear behind the enemies, you must turn the "invert sprite sorting" compatibility flag on.
Screenshots (slightly outdated) (taken on ZDoom 2.8.1):
Spoiler:Known bugs:
Spoiler: