You can do hanging crunches, pull-ups, dips, and push ups (not that you need anything to do push ups, but...)
I've used one of these before and got quick & great ab results.

November 17, 09

My new piece of exercise equipment just arrive. Woo hoo. I can't wait to put it together tomorrow and get busy using it. But for now, it's off to work...no time to enjoy it.