For about 40 years The Cure have been the main creative outlet for Robert Smith but he's engaged in the occasional side project here and there (and there). Whilst not as obscure as Cogasm or Cult Hero, The Glove and their sole album, Blue Sunshine, is a one album wonder that deserves better.
I suppose that The Glove were as much a Siouxsie & The Banshees side project as a Cure one, since aside from Smith (who was himself twice a Banshee) the Glove was full-time Banshee Steve Severin. They also came about largely because Siouxsie Sioux and Budgie were off recording their own Banshee side project, the first Creatures record. It also owed a lot to the neo-psychedelic direction that the Banshee's had first pursued with 1980's Kaleidoscope.