If you sand really small wood, metal, or plastic surfaces, this pen sander may be a HUGE time-saver.
From the product description
Proxxon 12-Volt Pen Sander sands linearly where space is at a premium. This superfine sander with linear sanding motion operates at 8,000 strokes per minute with a 3/32" stroke. Superfine finishing of wooden, plastic or metal surfaces can be done in less time hands can do without big efforts. It is ideal for surfaces, slots and tight corners. Included are four sanding attachments with straight shanks and four with angled shanks -four different shapes per shank style- as well as three sheets of pre-profiled self-adhesive sanding pads. The sheets are 180, 240 and 400 grit with 5 of each shape per sheet.
NOTE: To operate, this unit requires a 12-volt transformer such as the Proxxon 38704 Heavy Duty Transformer
Here's a link to more info on the Proxxon Pen Sander.