Recs.
Updated
The Perfect Multi-Gym Pro mounts on your door frame without the need for screws. It has padding on all surfaces that lean against the door frame, to protect your molding and wall.
Specs
Pros
Pro Easy to mount, more gentle on door frames
This pull up bar 'grips' your doorway from both sides, using a padded crossbar that goes above the top molding, and two padded supports that hold it on the sides on the opposite end. You don't need to drill any holes in your wall or molding to hold it in place, and the pads will protect your molding from dents and nicks.
Pro Easy to assemble
There are step-by-step instructions with pictures included in the box, and Perfect Fitness even provides the tool to put it together with (in case you don't own any Allan wrenches yourself). The included Allan wrench can be stored in the back of the molding crossbar, so you can easily access it when you need to tighten any screws on the pull up bar.
Cons
Con Wide grip too wide for people with narrow shoulders
The foam padding intended for the wide grip is right outside the frame rest, and for people with narrow shoulders it's just too wide (your hands should be just outside your shoulders when doing wide grip pull ups). For some reason, there isn't any foam in between the middle and outer edges of the bar, which prevents you from comfortably doing wide grip pull ups the proper way.
Con Might have to add extra foam to the pads to ensure molding doesn't get dented
If this bar stands at a slight angle due to the specifics of your doorway, the lower side of the frame rests can rub against the molding. Fortunately, you can do a quick DIY fix for this issue, by adding some extra foam on the lower parts of the frame rest by sticking an extra layer of foam over it.