Which low budget films with little publicity and low expectations became box office smashes?

There are numerous films that come to my mind, but Andhadhun is one of them. No one anticipated the film's remarkable twists and turns. There was very little publicity. When the film was released, word of mouth spread like wildfire, making Andhadhun an instant smash with both the general public and critics.

 

Tell me if you have any in mind.