A few weeks ago, my mom sent me one of those chin up bars that just grabs a door frame without any tools. I'm not exactly sure why she sent it (I doubt many guys my age get these things sent to them), except I made some comment a few months ago that I'd become a ghost of my former self, particularly with regards to upper body strength.
Anyway, it works far better than I would have guessed. I've been using it daily for a few weeks now. It feels sturdy and doesn't slip when you're using it despite the fact that it looks flimsy. I'm going to start taking it on business travel. Here's the gizmo. It looks cheesy, but I actually like it.