Story Builder is a writing site which enables the children in pairs to write in pairs.  The first child writes a complete sentence.  The second proof-reads with the help of the programme and finally music can be chosen to play in the background. 
Here is the link
http://www.docsstorybuilder.appspot.com/BV7uyo http://www.docsstorybuilder.appspot.com/BV7uyo

Regards
Lucie