So I've been developing a split-screen multiplayer FPS engine using LibGDX. It can handle up to 4 players.
Since (like most hobby developers) I can lose interest in a single project very quickly, this project contains several different games. The first game was a remake of the classic game 3D Monster Maze. However, I'm also working on a game of Tag, a Tower Defence game, a driving game, an FTL-type game and several others.
Source is here: https://github.com/SteveSmith16384/splitscreenfps_libgdx
Early example video here (Monster Maze level): https://www.youtube.com/watch?v=hM-P-M--Or4&t=108s