Sharing folders seems trickier tho. Wikipedia says
So I can't invite someone to a folder, I'd need to create sharing links for each file and sending them all to those who want to join the project...Files or folders can be shared privately with particular users having a Google account, using their @gmail.com email addresses. Sharing files with users not having a Google account requires making them accessible to "anybody with the link". This generates a secret URL for the file, which may be shared via email, blogs, etc. Files and folders can also be made "public on the web", which means that they can be indexed by search engines and thus can be found and accessed by anyone.