Q:

CodeIgniter - modular? 

I'm building several sites that need similar "modules."  For example, the sites may have the exact same login system, forum, etc. 
Is there a way I could build these modules once and just "drop" them in these various sites?  Some of the challenges I see:

Keeping the code consistent in the various sites.  Any changes made to a module should propagate to all of the sites using that module.  I guess I need a way to upgrade? 
Database: these functionality need to work as part of a bigger application.  Maybe the module needs to define relationships with other tables in its respective site. 

I'm sure there are more problems.  I think I should be looking at this: https://bitbucket.org/wiredesignz/codeigniter-modular-extensions-hmvc/wiki/Home, but I don't have any experience with it. 
So, I'm looking for solutions, suggestions, or more problems to this idea. 

A:

You can create and use third party packages by adding them to the third party folder (which is new for CI 2).  There is not much about it in the docs, but i found this. 
http://codeigniter.com/user_guide/libraries/loader.html
You can autoload the third party packages in the autoload file.  Packages can have their own controllers, models, views etc. 
Interestingly, Phil Sturgeon wrote a bit (http://philsturgeon.co.uk/blog/2010/04/codeigniter-packages-modules) about packages not being modules (in the strict sense of the term), but you could probably use third party packages for what you need.