Ask HN: Are there any good service for document management?

My new project needs document management, to allow customers to create documents and have the changes to those documents registered with an audit trail, and then have them shareable (but uneditable)

Obviously solutions like Google Docs & Dropbox exist, but this will be a service site with lots of users who each need there own 'workspace' so I need it to all be contained within our interface.

Do any good services, ideally with a REST type API exist for DMS?