This was a project very specific to my needs, but maybe you'll find it useful, too.

It is designed to fit in a lamp that I own that has tiered stands to put things on. There are 25mm posts at each corner and this organizer is meant to fit between two of those posts to kind of keep it in place. However, you could theoretically use this in a variety of different places.

The back slot is for a macbook pro 2013-2015 with a generic case, the middle is for the same laptop but without a case, and the last one is bigger than the back slot but fits maybe a book or an assortment of other things.

The idea is to print one side, then use the mirror function in your slicing program (I used Cura) to print the other side. Then, using 6mm-ish diameter wooden dowels, connect the two pieces to the length desired. Depending on your tolerances, you can choose to glue in the dowels or not.