Camp Nanowrimo is like a spin off of Nanowrimo.
Both challenges are the brainchild of OLL founder Chris Baty.
The concept in simple. Write a book in a month. It is not a competition as such, but there are winners and... not winners. To win the challenge you must write a novel of 50,000 words in one month. (Nanowrimo is in November and Camp Nano is in June and August) This demands you write 1667 words per day, but on some days you will probably write much less and on others much more. It is all part of the challenge. You can join other nanoers on the forums
The rewards, you ask? A finished manuscript that you have written yourself. (Plus if you do it in November and win, you get five free copies of your finished book.)
There is also a month (April) where you write a 100 page script. (script frenzy)
For younger writers, there is the young writers program of Nanowrimo and Script Frenzy where they can set their own goals if 50,000 words seems a bit daunting