i've always wondered about Lemmings 1 level editing. the L2 editor is excellent, but it would be really good to be able to make new 2 player levels for the original.
would it be a tricky task working it out then jotd? the files did look like gibberish when i looked into it before i must admit.
the best unofficial ones i can think of are Lemmings 2 and Cannon Fodder.