There's a Lemmings clone called Lix which has networked competitive multiplayer, but I don't know how it works. (I designed a few levels for the single-player

There's a Lemmings clone called Lix which has networked competitive multiplayer, but I don't know how it works. (I designed a few levels for the single-player mode which may or may not still be in the standard level pack, but didn't do much else with it.)