First off, if you don't know what Cave Story is, this should sum it up nicely, although this refers to the original one made only by Studio Pixel.
(I quoted a post from a member of the Little Fighter Empire forums)Originally Posted by The Lost Global Mod
The game itself can be downloaded from the Cave Story Tribute Site.
Spoiler warning:
The Cave Story Tribute Site Forums is where the mods are, including two of my mods (although I am working on four mods at the same time).
EDIT:
... Guess very few know about Cave Story...
That or I'm too impatient.