The Pancake Development Kit allows you to extend, and add features to Pancake. It's meant to be used by a computer programmer to make a game, a utility, or whatever for Pancake. It is right now geared more towards Pascal, but a C interface could be made from the Pascal. An example external is provided to show you how to make a command that can be called from the main menu.
Readme - Gives you an idea of how to write externals.