Gears of War PC Edition comes with the Gears Editor, which pretty much boils down to being a level editor... It's a level editor in the sense that UNREAL EDITOR IS A LEVEL EDITOR, though, so you'd best have time to learn your way through it. You can make some REALLY impressive stuff with it, though, and it's all shit that looks GREAT on a resume if you want to go be a level designer or something.
And, yes, this is true. My roommate is working for Midway right now and they were very impressed by the work we did on the Gears level we made a few months back.