Help please!

Working on several bids at the moment - great way to spend the summer! (yes yes - what summer?!) anyway, need some help - we all get so confused with the 'versioning' of documents that I am desperate to find some on line system of collaborating that really works and really takes the pain out of all this - thought I'd found the answer with Scribd but then discovered you can't edit on line - so it's not really collaborative at all - are there any other good and user friendly sites - does anyone know? is there anyone out there?