megmorsie uses CodeIgniter
I used CodeIgniter while working at KHM Travel Group. It was the system we used for an affiliate-based site called TravSearch, which I later replaced with a WordPress Multisite. I developed a .csv upload form to transfer all the information from the affiliate table of CodeIgniter to the user and options tables in WPMU.
gllona uses CodeIgniter
CodeIgniter is the MVC framework used for the PHP coding. Also, validation criteria for (database) table fields are the provided by CodeIgniter, and signatures for others are derived from those.
delbin uses CodeIgniter
It is super easy to do things in PHP using codeigniter. Used the MVC architecture to create different types of pages and modules.