Bluebeam has a cloud-based feature called Bluebeam Studio that allows documents to be store in the cloud and be available for markup from multiple users. Studio is broken down into categories: Project and Session. I know that there are pieces of information out there that compare these two features separately, but I do not believe that they go in-depth enough to give a full description of what is differences between them. Some of this is just putting my knowledge out there, however, I assume in 6 months I could possibly be able to give more differences.
Project is designed to allow users of the project the ability to check-in and out documents for the purpose of making changes. The best comparison that I tell people when trying to explain projects is that the idea is like checking out a library book to do the work. Project requires a license to create a new project and perform tasks other than viewing files. While a document is checked out, no other user can make a change to the file. Individual file(s) can be broken out into a session and then brought back to the project when finished. Project also allows the ability to recover a previous revision of the file. Project allows the ability to upload file types other than pdf, such as .xlsx and .doc files. I would defer from using it for Microsoft file types as Office 365 and Google Docs has much better collaborative abilities for these file types. Project also allows multiple signatures on a document without the need to save as to a new file.
I would recommend that you look into adding Set files(.bex) to your project arsenal as it is an ideal free tool for managing up-to-date Drawing Sets (Stick or Conformed Sets). Sets are an entry all on their own and I am sure I will write about it at another time.
Session, while similar to Project, allows multiple users to concurrently markup a document without the necessity of checking in/out. When I am training people, I always relate this to kids in a sandbox, they can all be in there at the same time and making a mess. The only difference is that no one can stomp on another's sandcastle, as Studio Session does not allow others to modify each other's markups. Session only requires a license when creating the session and adding documents, however, not for creating markups on documents. It works well when working with others(clients) that do not have a Bluebeam license. Due to the concurrent markup feature of the software, it does not allow any type of revision history. It also does not allow modifications to documents such as signing, page rotation, or renaming. A session is limited to only being able to upload pdf files. A Session does prevent a user from being able to modify/delete another user’s comment while the file remains in the session. Session can contain multiple documents and keeps a history of who has entered and left a project, history of modifications that have happened and by whom, as well as a chat feature that can be archived upon closure.