drum sander

Similar to a belt sander, a drum sander consists of a loop of sandpaper wrapped around a semi-rigid drum. This can be either a stand-alone tool, or an add-on for an electric drill (Which can then be made stand-alone by putting it in a drill-press). Care must be taken when fitting the sandpaper, as it has an overlap which must be fitted so that the outside is in front of the inside piece¹ - like so

          
              <-- Drum rotates this way.                      
     \  inside layer                /
      \           =================/
       \============ Outside layer
=====================================Piece to be sanded 

Drum sanders are most useful for sanding smooth curved surfaces, where a flat sander would be no use. The drill add-ons are quite cheap (under £10), and can be used in the same role as a belt sander. For diy use, this is probably the only sander you'll ever need.

--

Thanks to Ouroboros, who points out that there are also movable drum sanders, used for refinishing wooden floors. They look like a lawnmower, or scarifier, and are used on floors that are severely beaten up. To merely take the varnish off a floor, you'd use an orbital floor sander, which looks like a floor polisher².

1 - If you put it on the wrong way round, it unravels. Damn.

2- There was an episode of hang time where in an effort to get in coach's good books, they attempt to polish the gym floor. Unfortunately, they use an orbital floor sander. d'oh!

ref - http://www.easy2diy.com (Refinishing hardwood floors with a drum sander).