What to use for a CodeIgniter Backend

The back-end is one of the things that drew me to Bonfire. It does have some conventions and inter-related modules which can constrain interoperability with existing back-end code, but most of it is designed so that it can be overridden. It is also designed to use jQuery and Bootstrap 2 (though a Bootstrap 3 branch is available, it's a little out of synch), but I have a long-term goal of at least making it easier to replace the JavaScript/CSS framework used by the back-end theme.

Another of the reasons I chose Bonfire was being able to easily incorporate my own modules into the back-end and still have the code in separate locations from the Bonfire code. It overrides some of the core and HMVC functionality to insert itself as a sort of secondary "system" layer, so the majority of the code stays separate from your application, but can also be overridden by your application.

However, I chose Bonfire at the beginning of my project, when I had nothing to integrate into it, so I'm not really sure how difficult it is to work with when trying to merge it with existing functionality.

Bonfire

Practical CodeIgniter 3
CodeIgniter Testing Guide