Binding inserts are an easy way to share bindings on several pairs of skis - you can ride a pair of touring skis with two different sets of bindings, take resort skis on the occasional tour, or just buy lots of skis and not have to mount multiple sets of bindings. They've been on the market for awhile now, but some folks don't know just how easy they are to install yourself! Especially if you've already had the holes drilled in the ski... 

There are two companies that manufacture the inserts, as well as offer a selection of tools and instructions on how to best install. Quiver Killer and Binding Freedom inserts are very similar, but Binding Freedom inserts are easier to install because they have a notch at the top of the insert which allows installation with nothing more than a flathead screwdriver. More in DIY installation here. If you're hesitating, most ski shops will do the full install for you for under $100, but with pre-manufactured tools designed specifically for the job (like the bit pictured below), its a project any ski bum can become proficient at.