KKAPI is a project that aims to make creating mods for Kokatsu! easier and less bug-prone. It abstracts away a lot of the complexity of hooking the game save/load logic, creating interface elements at runtime, and many other tasks. All this while supplying many useful methods and tools.
Here are some mods that use KKAPI:
Koikatu Overlay Mods - Uses many different features like saving to coordinates, partial load toggles, advances maker interface elements, using Windows Open File dialogs, etc.
KK_BecomeTrap - Simple mod that give a good example of how clean and easy KKAPI makes things.
KK_SkinEffects - Uses StudioAPI to create custom controls in the studio interface.
KKABMX - Uses a lot of runtime-generated maker UI elements, fairly complex.