The Rolleidoscop was made from 1926 to 1939 in Germany alongside the Heidoscop, the same camera but with a sheet film or glass plate back. It was actually the very first camera that renowned manufacturer Rollei made.
Rumor has it that many photographers used these as a regular camera because the quality of lenses were so good for the era. They would cover one of the lenses and take a photo and cover the other lens for the next photo without advancing the film, making two... more