Beal Escaper

Now, whether you're climbing, mountaineering, canyoning, or freeriding, you can abseil the full distance of a rope without having to leave it behind. If one of your ropes become damaged, you have to bail, or you simply want to save as much as weight as possible, take the Beal Escaper, loop it through the anchor, attach it to one end of the rope on a bight, then descend as normal. When you're at the bottom, tug the rope until it's free. (As you can see from the above video, it takes around 15 pulls until the rope falls.) The Escaper locks the rope in place when weighted, but when repeatedly weighted and unweighted, it loosens. That way, you can retrieve your rope.

It is of course recommended that you become fully familiar with this system before using it for an abseil.