This goes right up there with "hey let's make a movie with a virtual studio across the internet" but since I just found the link I may as well put it down here for when I get those megalomaniac impulses.
Unreal Engine used to make gears of war etc free developer's kit. Here
apparently a pretty easy engine to use and mod and have pretty reasonable royalties: US$0 on the first US$50,000 in revenue, and US$2,500 on the next US$10,000 in revenue)
walk thru setting up a easy game
time time time
never enough of it