By default, Codeigniter is setup to run a single application. Since each controller can reference views located in organized, separate folders, an entire website could look like it uses multiple applications. For example, a controller called blog.php could access view files in the views/blog folder. With a single application that requires one database this could work just fine.
Another method is to use multiple applications. To do this, you simply remove the contents in the application folder (or copy and paste the contents into a new folder with the application’s name). The application folder can store various folders for separate applications which all can run off any desired database. Each application folder will hold the usual folders; config, controllers, errors, helpers, hooks, language, libraries, models and views. Each application will use the core Codeigniter files and even use the same css file too.
After the folders are moved, the next step is to adjust the index.php file for the main application which should contain the home page, and various others if desired. The index.php file will have $application_folder = “application”; changed to $application_folder = “application/app1”;
Each other application will use another index.php file with a different name. The easy way to do this to open the index.php file and change $application_folder = “application/app1”; to $application_folder = “application/app2”; and save it with a new name like index_app2.php
Now, both apps can be used. The website address like yoursite.com or yoursite.com/index.php will display the app1 application while the url yoursite.com/index_app2.php will display the app2 default controller.