Well, to list stuff off, basic file handling, a simple implementation of ini files, a simple loader for png files, a system for keeping track of texture pages and drawing what's on them, a system for caching text and drawing it, a generic game loop minus the actual update or rendering functions, an event handler for sorting input into easily checked state, a dialogue system using the drawing and text systems, a core base for making menu with no default, a collision system, and a system for keeping track of audio resources (mainly how long they've been playing and how many instances of sounds are current). These are all in separate files, but the drawing portion, the game loop and the event handler are closely tied together. Part of why I'm unsure is that all the things the programming does are things rpgmaker and most other "engines" do as well.