You're probably familar with the 30-day version of the popular National Novel Writing Month, but have you heard about the 3-day Novel Contest? It's publishing version of the New York Marathon.
The contest has been in existence since 1977 and many of the winning entries have been published.
"...writing must begin no earlier than 12:01 a.m., Saturday, August 30th and stop by midnight on Monday, September 1st. Novels may be written using any method, and in any location, anywhere in the world."