Hey all,
I have successfully incorporated Steam connectivity in a 3D engine and even made a simple platformer prototype using it (here is me and my friend playing it:
The idea is to support a large number of players and to require a small amount of resources. No giant worlds or dozens of characters or animations or anything. I can recolor and edit resources though (so I can have different color teams and whatnot).
My first thought was a simultaneous board game with some interactivity between players. I could also do a game like Town of Salem (but different). Not sure if a multiplayer (3+) card game could be made to work. Or dominoes. Games like Master of Magic/Orion/Civ are both beyond my skills and resources.
What other turn-based multiplayer games are worth considering?