It would be very useful for people working on terminal utilities, graphical apps, or the window manager itself if we had some sort of general UI Guideline to dictate when certain elements should be used, when command line applications should prompt and when to read from STDIN, general design principles, etc. This isn't probably going to be necessary for awhile yet (if ever), but its something to think about. It doesn't have to be long and kinda useless like the Apple one either, it could just be a simple Markdown document provided with Serenity.