The L4D splitscreen wasn't a mod. The code already exists in the retail version. You just had to enable it. But there seems to be a 4-player splitscreen mod for the pc version of UT3. Since Borderlands was build on the engine of UT3 you still can hope.D4zZ said:There will be a mod soon enough.
L4D has splitscreen, that is the most recent one I can remember but I know alot of splitscreen mods exist.