Anyone who uses 3D CAD software needs a 3D mouse!. I have the 3Dconnexion Space Navigator, and this Thing is a wrist rest surround for it.
It is in two parts which hold the 3D mouse in place to make it more comfortable and more like the premium models. Also allows access to the two side buttons.

Materials
-2x M5x40 socket cap head bolts
-2x M5 nuts
-4x 18x10mm pads (cut some rubber or sticky foam or similar)
Instructions
-Print the .thing or .stl. It is two parts that print together to self support.
-On Replicator 2, I used 0.3mm layer, 10% fill, no support , no raft
-As there's a large flat base, you'll want to print on blue masking tape to prevent it sticking to the build plate
-Glue pads on the base into the 4 recesses. I cut some 4mm rubber and glued with superglue. You could also use stick foam or something like that. You want to make the base really stable so it wont rock or slide on the desk.
-Insert your 3D mouse into the main body. Add the base and secure by dropping the nuts into the slots, then screwing the bolts in through the holes in the back.
Notes
-You will get some stringy bits where your printer prints the arcs with nothing below it. Don't worry, the printer will sort itself in a layer or two and you can just cut them off
-You could glue the two parts together instead of using bolts, though of course that's more permanent!
-You may have to sand down the edges around the side buttons slightly to give good access for pressing