I own a Ikea-pen holder on my desk which I like very much, but It has one very large compartment in the front, where I wanted to put my markers. Since I don't have enough markers to fill the whole compartment, I designed a small box in openscad and printed it on my makerbot - et voila! a smaller compartment for my pens.
The box is for sure not the biggest innovation in 3D desgin and I could have used cardboard boxes too, but I really like the idea using a 3D printer to personalize off the shelf furniture :-)
3D printed Heptagonal-Finger-Ring
Generative Battery Compartment