This is a simple holder/organizer for pens, markers and such which mounts to your monitor with velcro or double-sided tape. It will hold three pens or markers along with 2 up-to-an-inch-wide-things.
This was directly inspired by https://www.thingiverse.com/thing:3124667, but I wanted something smaller, both for easier printing and to be less obtrusive. (This one should fit into most printer build-volumes, and takes "only" 65 grams of material and 5 hours 15 minutes on my Monoprice Ultimate.)
I recommend printing with 2 walls at 0.5mm, which (given inside and outside surfaces) will precisely fill the 2mm cylinder-wall thickness. (3 walls at 0.4 would probably also work.)