Specifically designed for the Printrbot Jr., this cup mounts to the left of the Y/Z axis carriage. It will hold pens, exacto knives, tweezers, pliers, etc. Anything you want to keep close by.
Three versions are available. I wouldn't recommend the "cut out" version, unless you're extra-adventurous. That was my original design and it turned out bad, but I wasn't going to print it again.