Notes.Westsidenotes.com's social networking engine, Elgg software from https://valueapplications.com/AllApplications.aspx?prog_id=253510 is designed to run at the heart of your socially-aware application solution. The software has powerful, granular, privacy controls for users.  Content can be marked by a users as public, private or only accessible by select "friends' or pre-defined groups.

For a good example of contolling access, check out the Pages Plugin that allows you to save and store hierarchically-organized pages of text, and restrict both reading and writing privileges to them. This means that you can collaboratively create a set of documents with a loose collection of people, participate in a writing process with a formal group, or simply use the functionality to write a document that only you can see, and only choose to share it once it's done.

The easy navigation menu allows you to see the whole document structure from any page. You can create as many of these structures as you like; each individual page has its own access controls, so you can reveal portions of the structure while keeping others hidden. In keeping with all other elements in Elgg, you can add comments on a page, or search for pages by tag and so much more.