Template Game 3D FPS 
This is an Open Source prototype game example for the Modd.io Community.
You can take it and do whatever you want with it.
https://www.modd.io/play/3dfps/
Moddio does not yet have all the features required for a complete 3D FPS game, but they will probably be added in due time.
This can provide a good starting baseline for anyone who wants to make such a game in the future.