I do a lot of free-standing "holders" from industrial (5 ply) cardboard and hot glue. Surprisingly sturdy! Made a video about this too: https://youtu.be/s-aNW3h15K0 - all of these are still in use and I made more & more complex ones too.

Seems the calculator is designed for a "collection of boxes", which I guess is a start, but when I hear "organizer" a collection of separate boxes ain't what I want. The most significant factor of making one's own is that it's 105% customized to the need, no more no less. That means usually a lot of thought between "target place bounding box" vs "bounding boxes of things the holder shall hold".

For "organize a drawer, quickly!" I got myself a couple of sets of "modular" boxes - they have little tabs on their sides so one can snap them together like lego.

Poor/clever man's Gridfinity

Foamcore is truly the world's best "around the house" material for quick projects. An amazing trick not used for simple boxes in the parent post, is to simply score the fold-lines of a box and then fold the foamcore into the shape you desire, instead of cutting all the edges. It makes for very fast and fun crafting.

My favorite activity I ever did with foamcore was to make a to-scale layout of an apartment my wife and I were moving into so that we could experiment with simple to-scale rectangles as stand-ins for furniture to figure out our layout.

What a wonderful material!

Foamed plastic seems underappreciated in the age of 3D printing. Recently I was researching foamed PVC sheets to make Raspberry Pi contraptions. Seems I'll have to buy them online, though.