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)<p>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.<p>Do any good services, ideally with a REST type API exist for DMS?
SharePoint from Microsoft offers all that features. They have also cloud services like OneSpacePro, Office365 for business. You can access the data via WebDAV (<a href="http://en.wikipedia.org/wiki/WebDAV" rel="nofollow">http://en.wikipedia.org/wiki/WebDAV</a> ) and API.
I would look into Box.com which has been working to differentiate itself as being able to have audit logs, be things like HIPAA compliant, etc. They also had robust APIs last time I looked. There's also always AWS S3+AMI if you're willing to do more of the heavy lifting in terms of interface.