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:
This is actually really cool. You should make sure that this comes up when just searching for cat stuff, maybe a cat owner doesn't know the original product exists and can now make their own instead of buying one.