Very nice suggestion!
I am going to think about that.
Thanks a lot!
EDIT: I got an idea: you could try moving your project to a folder that is shared with DropBox with multiple people.
DropBox can share and synchronize a folder between two or more computers, so that the content of the folder remains the same on all the computers where it is synchronized (i.e. when a user adds a file on one computer, it is copied to all other computers, etc).
This way you should be able to work with your friends on a common Adventure Maker project. As long as you don't work simultaneously on the same frame, it should work fine!
I haven't tested it yet though. If anyone tries this out, please let us know the outcome...