Bruin! It's BIG FUN!
If you can't spend a month on NANoWriMo, then this is a compressed, super-duper, version.
1500 words upwards between 12am and 8pm London time (the deadline isn't as strict as it could be) and the novels (generally 2 or 3 versions) are released just before midnight.
No one has any idea of genre - until just after midnight on Saturday, when you get emailed a brief. Each author receives the same brief, EXCEPT for their chapter. You get a slim 'this is where you are in the story' a more detailed 'this is what has to happen in the chapter' and a short 'this is how the chapter ends.' Other than that it's entirely up to you what you write, and what the characters get up to. Considering no one knows what anyone else is writing, the resultant novels are remarkably coherent .
The best explanation is at: http://novelinaday.com/
I hope you sign up! PM me if you want a copy of one of the previous briefs.