The Holga 120S is the basic version of the medium format 'toy' camera that has recently become ultra popular. The camera is poorly made, everything in it is plastic, including the lens and this leads to blown out, wild looking photos. The worst optics ever produce some of the most striking images- this is lomography at its best.
You can get Holgas moddified to do differnt things with different features. For instance some can shoot 6*6 and some only 6*4.5, others have been modded to include cable releases, tripod mounts, and to shoot 35mm amongst others. Holgamods.com explains the common mods and what they do