I've had this half-idea for recreating something like Garry's Mod in Godot for a while now. It seems like something someone would have created by now but it doesn't exist yet for whatever reason.

Like, a framework for building first-person FPS-ish game modes and handling all the asset management, sync, etc, like GMod being built around Source does and just letting developers build the game modes without worrying about the annoying tricky stuff.