well I've got a few games but I only play a few of them right now. One could possibility would be America's Army, since it's absolutely free so everyone could download and play. It also runs on crappy machines so that wouldn't be a problem either.
I'd also be willing to play bf2.
America's Army is fun, but it get's old, and updates take FOREVER. I think I got to like honor 14 before I got sick of it. The only map I played was Bridge Crossing, and that was a damn sweet map.