This is a great collaborative tool that we have used in class so you should have a little experience with it. Google doc is easy if you are familiar with a word processor program.
Dropbox is an easy way to share files and to back them up. You can access your docs on any computer even without the software installed. You can send an invite to share access to specific folders or files to allow collaboration. It works on multiple platforms including iPad/Pod/Phone, PC, MAC, Android, Linux, and Blackberry
The account holder holds the control of this tool. A user doesn't have to download documents to the computer to view them. It has ways to plan ahead through task management, group calendars and a birds eye view of a timeline. It has a discussion board. Information can be share easily.
My students can finish their lab report together. The students can add info as they need to at the same time as their peers to allow more time for other things.