During many of my late nights catching up on TV I often see an infomercial for the "Iron Gym" pull-up bar. They claim it attaches (non-permanently) to any door to create an instant gym. Well Santa was good to me this year and I got one. I must say I am pretty impressed. I thought for sure the product would not be as nice as they portray it in the commercials. But after getting it assembled, it worked on the first door I tried it on.
Granted some paint started to crack around the door frame from my weight (about 200 lbs) pulling down on it. But I now simply use it in my closet door frame, and it works perfect. It doesn't even crack the paint around the door frame there. So it may have been an exception when that happened on first door. According to the instructions it requires a door frame that is 24" to 32" wide. It also requires that you have molding around the door frame as it uses the top molding to help latch on. It has a maximum weight of 300 lbs. Like I mentioned, I'm around 200 lbs and it is very stable for me.
I'll be attaching a photo of mine so you can see how it looks. It really does a great job of distributing the weight off of the frame by having much of the pressure be on the horizontal pads that press against the sides of your door frame. Though I have only used it for pull-ups, it can also be used as a push-up bar, a sit-up bar and for doing dips. Pretty slick. My wife got mine for like $30 at Walgreens.
If you have wanted one and wonder if they work, I would definitely recommend pulling the trigger and getting one. I've been very impressed. It is a stable, sturdy workout tool that is really easy to attach to your door and take down when you are done. If anyone has any questions, let me know!