There are a lot of 48-Hour film competitions out there. They are usually a contest in which teams of filmmakers are assigned a genre, a character, a prop, and a line of dialogue, and have 48 hours to create a short film containing those elements. Shortly after the 48 hours of filmmaking, the films are then screened at a theater in the city. The most famous one is the 48 Hour Film Project, a wild and sleepless competition, created by Mark Ruppert and is produced by Ruppert and Liz Langston.
In 2012, over 50,000 filmmakers made almost 4,000 films in 120 cities on 6 continents around the world. Over the 11 years of 48 Hour Film Project over 19,000 films have been made by 278,000 people. You can see press about them here.