Master - Main Testing and Development.
Core Files - Just the main files needed to get you going.
CI-2 - Working with Codeigniter 2
CI-3 - Working with Codeingiter 3
This is stupidly old but someone asked me why ? How did they even find it for a start... Because why not and it was the old version working on CI 2 & 3, big deal in the day, useless now lol, unless...
We make it fun and do CI4, because why not haha