moojelly - SML2 and SML3 level editor
This editor written in C++ works by extracting the levels from the original ROM, modifying the data, then patching it back into the ROM. This means that you can play it on the original hardware just as if it was the original game.
The eventual plan is to make a complete user made sequel to SML2 (and then maybe also SML3). So any help is very much appreciated, either by helping develop the editor or by submitting level designs (when the editor is completed).