I wanted something to elevate my MacBook Pro off the table so it could get a little airflow. I didn't really want to change the angle that much, just get it off the surface so it wouldn't get so warm.
I made it so it clips in on each side using the small recess the keyboard sits in, that keeps it tightly on the MacBook Pro so it doesn't slide around. I printed it out of PETG so it has a little flex when it pops on and off the sides.
I printed two, of course, but mirrored one of them. Print it on its side with the triangle's base (the wide part) near the bottom, just like the photo of the finished part. No need for supports. It might print on the back flat side (the part that faces away from the Mac when installed) without issue, but I haven't tried that yet. It'll be stronger printed on its side due to the layer orientation at any rate.