My CodeIgniter setup follows the usual scheme — a user app, and a second app called ‘admin’ that is one directory-level down. As I understand things, it’s presumed the end-user will want his/her own interface, probably one with less public access; so you have ‘admin’.
But Model and Library functions will often be the same for both. That means maintaining duplicate files so both apps are provided for — with all the tedium and risk inherent in redundant code.
How do you consolidate your functions?
Having researched more, it looks like this is roughly a duplicate of:
multiple applications with codeigniter from same framework directory?
… which references this:
http://codeigniter.com/forums/viewthread/136321/
… and also relates to this:
http://ellislab.com/codeigniter/user_guide/general/managing_apps.html