Framework for storing 35mm acrylic paint bottles (FolkArt, DecoArt, Nicoles's, Golden).
I've found that this size is very common, and accommodates Scene-o-Rama bottles, Sculpey gloss bottles, bake-n-bond, liquid clay and more.

Included STL files for 1 cell, 4 cells, and 10 cells. There's also an insert piece to size-down cells to hold smaller dropper bottles. These clusters can be printed with no supports or a simple support inside windows.

The windows reduce overall filament use, make it easier to remove bottles, and help identifying bottle labels.

The design is planned for use in a supply drawer, and is meant to be nested with multiple
large clusters for the overall shape and supplemented with small clusters or individual cells as needed.

Bottles can be stored with the tops up or down.

Additional design possibilities with this framework:
1) By pressing 2 clusters together, it's possible to create a simple 10-bottle carrying case solution (rubber band recommended too).

2) Vertical standing solutions are possible with a bit of hot glue, or by combining clusters in meshmixer, blender, etc before printing. Inserting bottles cap-first is recommended to keep the structure balanced. I'd also recommend gluing whatever structure you build to a base, though--the design gets a little front-heavy.

3) Mounting options are supplied for the cluster, with M4 holes at 2 ends and at just 1 end. Bear in mind that paint can get heavy, so if you're planning to mount horizontally and to connect multiple clusters, it's be wise to make the combinations in software rather than relying on glue to hold everything later.

4) For inverted bottles, I just flip the frame over. You can also, however, glue dowels between a few intersections to elevate the frame and mount bottles inverted with the frame held in the air. This would provide some added stability (if you're putting these in a drawer that gets violently opened frequently, for example).

Largest cluster is 7.125 inches by 4.8125 inches (180mm x 98mm)
Smallest inside dimension of each cell is 35mm.
Circle cutout in the base of each cell is 29mm.

UPDATE: I have added a printable insert module to reduce the pod size for typical (25mm) dropper bottles.

If you need an exclusively dropper-bottle rack, it would be wasteful to use this design, but if you have a variety of craft bottles and need to mix in some droppers, this insert allows you to easily add them to the framework.