These are fan-made modifications to the original Pokmon Mystery Dungeon: Explorers of Sky game. They alter various aspects of the gameplay, story, or visuals through code manipulation, typically distributed as patch files to be applied to a legitimate ROM image of the game.
Such alterations offer players enhanced or entirely new experiences beyond the constraints of the original game. This includes fixes to existing bugs, difficulty adjustments, story expansions, character additions, or graphical improvements, extending the longevity and replayability of a popular title.