This mod for SRB2 just got released. Aside from some connection issues, it's pretty fun. Also, don't play it with the OpenGL renderer. There's a bug that can render you completely unable to see anything, even the menus, and you have to restart the game to fix it. There's no single player beyond time trials, either, unfortunately.
Download: https://mb.srb2.org/showthread.php?t=43708
You'll need SRB2 to play it, obviously. Be sure to pick up the extras pack, if you want more than six playable characters.