Symbyoz. I signed up and created a goal page but sadly I can't seem to get access to it today. Perhaps there's an internet problem, but the stuff I did yesterday seems to have disappeared. not a great start.
The concept is simple enough. You create an idea and other people can comment. There are tabs for people and resources and you have your own ideas and network ideas. There is no facility to add files to share.
In the end I think it will be a preference thing, not withstanding today's lost idea issue, between this and say Writeboard, that does the same sort on thing and does it well.
Reviewpad. Now this looks very promising. Easy to navigate, able to add files (in fact you can't crate a "pad" without adding at least one file). Actually the whole point fo Reviewpad is to give you a place to review files with others. You can add comments, give permission to download the file and all with a free account with 500mb of space. You can even save a pad as a pdf which show everything including all the file contents. So if you wanted to, you could take a pdf version with you your mobile device to read on the train! No internet access required!
In looking for something simple and easy to use for less adventurous partners, this might just win the day.