Have recently been tinkering with Alfresco and WebDAV repositories and so have updated Elena's repository behaviour chart to include these.
A couple of notes which may be relevant.
1. The WebDAV repository interface *may* (i.e. I have not yet tried it!) be a way to connect to Moodle 2.x to SharePoint as a repository. For example, see the first part (Step 1) of this Microsoft Education Labs white paper on how to set up a SharePoint document Library with a WebDAV interface.
2. In general, repositories with a WebDAV interface (e.g. SharePoint, Alfresco) may simplify things for users. A folder or drive in the user's desktop/file-system can be mapped to the WebDAV repository. Then users can add/edit files in this folder and they will be immediately available to Moodle via the repository interface, file-picker etc. i.e. users don't (necessarily) need to directly use SharePoint or Alfresco at all.
Neither of the above are complete solutions (still need to set up the external repository or repositories, set access permissions etc), but I hope they offer 'steps in the right direction'.