I'm in the planning stage of a GUI library based on my aurum-display library. I'd like to write a demo program along with it, but I'm not 100% decided on what. I'm currently leaning toward a text editor. Text editors can vary greatly in complexity, so it can start out as a Notepad clone and grow into something more featured if there's any interest. Other than a text editor, what else would be a good small to medium size project to demo a GUI library?