In keeping with my usual tradition of harping on about the dumb shit I design and slap up on Printables:
https://www.printables.com/model/862518-cat-shelf-bracket-for-smartykat-paw-perch-or-build
These brackets solve a specific, but major, usability issue with the aforementioned brand and model of cat accessory widely sold at Walmart, Amazon, Chewy, Pet Smart, etc.
Conversely, there's nothing stopping you from screwing your own piece of wood to the top of a pair of these and arriving at roughly the same result without shelling out 30 of your hard earned Washingtons.
Cat tax paid:
Wow what a major oversight on the company's part. How is it possible that every single one of the dozens of people who put this product to market all coincidentally don't have windowsills? Like they must have had to go out of their way to find a house that would work for the box art.
Your model is elegant and brilliant. Awesome!