Since Mari0 is suddenly popular, I guess posting some information will be useful.
Yes, this is an actual game being developed - it is not a mod of any existing one. It’s coded with Löve (info at the bottom of the left menu) and will be released for free (so we don’t get stabbed by lawyers)
All the source code of the game will be available after release
The game will have mappacks, which will be downloadable from ingame. Users most likely won’t be able to publish maps directly, but will be able to send them in and we’ll add them for everyone to use.
The primary maps will have a story and some portaly puzzles. What kind, well, we’ll figure that out as we go
Level editor will be embedded in the game so you can edit the level while you play
Original SMB levels and Lost levels will be included