Brain Annex may be used as a standalone web app, or used to power other web apps.
The new, overhauled version 5, is currently in late Beta.
Its Programmer's Guide can be found here
See also the README file
Obsolete version 4
1. Brain Annex Plugins (v. 4)
2. Content Management (v. 4)
3. Login Management (v. 4)
4. Technical Overview (v. 4)