My wife asked me to make a try to hold some pins she's been collecting. These pins come on square cards that fit nicely into a 3.5" by 3.5" space. So I made her a tray with 4 sections. Then she wanted a few such trays. I pointed out that it might be nice if they were stackable, and she eagerly agreed to that. Then she had something bigger that wouldn't fit into the smaller spaces, so I made a variant with a single space (no dividers). Then she asked for a lid. Then she asked for a tray with 2 normal small sections, and a third section that took up the rest of the tray.

I made all of this in the basic 3D Builder that comes with Microsoft Windows.

So here's the result. I have variants with 1, 2, 3, or 4 sections. Each variant comes either with tabs at the top to make a neat stack, or without. There is also a lid either with or without the tabs.

I normally print these at fairly low resolution (200nm) and it takes 8-10 hours each. The bottom is a little thick, I know, but I like making sure the tray and stack will have enough rigidity; so I do use infill and only at 15%. Supports are not needed, even for the tabbed versions, but that will depend on the printer.