These are Furniture joints to make your own self-assembled furniture without screws.

 I made several angle combinations so you can make shelves, desks, etc. Even libraries!

Its a final project for a 3D printing couse i made back in 2017. I uploaded it on Thingiverse, since then it has done quite well (more than 17.000 downloads!)

Here's the link https://www.thingiverse.com/thing:2400175