My daughter likes to keep her markers organized, but the box they came in deteriorated quickly. This is a customizable snapping holder for markers, with a spot to hold the cap while a marker is in use. Would likely attach nicely to a vertical surface using a command strip or something.

To customize and render this, you'll need to download the SCAD file and open it with OpenSCAD (free). Edit the dimensions at the top of the SCAD file for your size of markers, then press F6 to render it and F7 to save an STL file.

The included STL is the one pictured.