This is a tray to hold 15 dropper paint bottles (such as Vallejo or Army Painter brand paints). Three trays will fit into an ArtBin 12" Deep Base Carrying Case (link below) for a total of 45 bottles per case.
This was inspired by https://www.thingiverse.com/thing:2024692 but I wanted the ability to work with some paints without having a large tray in my work area. I landed on having three smaller trays instead of 1 large one. While not as an elegant design as theirs, this will allow you to lift a tray out to work with up to 15 paints per tray.