Viewer:
Can view a Project
Can add comments and respond to comments with the Comment tool and participate in votings
Can not edit, share or delete a Project
Editor:
Can edit a Project (including commenting and voting)
Can not share or delete a Project
Manager:
Can edit and share a Project (Add other users to a Project)
Has additional options for Connected View to better coordinate groups of participants
Can not delete a Project
Admin:
Can edit, share and delete a Project permanently.
Has additional options for Connected View to better coordinate groups of participants