Kinoautomat (1967)
Kinoautomat (1967) was the world's first interactive movie, conceived by Radúz Činčera for the Czechoslovak Pavilion at Expo '67 in Montreal. At nine points during the film the action stops, and a moderator appears on stage to ask the audience to choose between two scenes; following an audience vote, the chosen scene is played.
More at Wikipedia.