It's a die made by a company called The Cat's Pajamas. It's very slim and lightweight, plus instructions are printed on the backing for Cuttlebug, Wizard, or the Big Shot/Big Kick.
It was really easy to use with my Cuttlebug. There was some double-stick tape left on the back of the metal die, so I used it to keep it in place on the plate. I lined up the edge of my card next to the edge of the die, and it cut it beautifully! I'm so thrilled to be able to make these lovely bracket shapes on my cards and for scrapbooking embellishments.
The result (and I will get it decorated soon, I promise!):