Need Halloween decorations or camping gear? L.A. startup Joymode wants to be the Uber of that.

Apps have helped people share their homes, cars and technical skills. But stuff - specifically, the kind that spends most of the year in garages, closets and sheds - hasn't proved as easy to share. Enter Joymode. Rather than own stuff you'll seldom use, the start-up offers on-demand rentals. Planning a beach party?...