You're going to have to start with the database directory and either analyze the requirements or add files to fix errors as you go. Since it wasn't designed to work outside of CI, I don't know if you'll find anyone who can tell you definitively how to get it working on its own. For a start, though:
- Unless you modify the scripts, BASEPATH will need to be defined to load any of the classes
- You'll probably need to create replacements for show_error(), log_message(), load_class, and some of the other functions in /core/Common.php and CI's loader
- DB is going to look for the config file and expect APPPATH to be defined
- CI_DB_driver's display_error() method uses load_class to pull in the Lang and Exceptions classes. If you don't create replacements, you'll run into things like Lang->load() calling get_instance() to access the loader and Exceptions->show_error() looking for templates in the application errors directory.
