FFcast deals with rectangles on screens. Mostly, it selects rectangles. Like most boring jobs, there are many ways to do it: free selection, selection by window, screen number, numeric geometry, or by edge detection. Simple arithmetic operations allow simple combinations and adjustments. Now FFcast knows all about these rectangles, but what to do with them? Well, like most useless things, there are many ways to use them: in practice, screenshots and screencasts are obviously popular options; in general, the geometry can be utilized by any application that understands X geometry, including window managers, xorg-apps (xclock, xev), byzanz-record, dunst, dzen2, FFmpeg, gifview, ImageMagick, maim, mousetweaks, mpv, Nautilus, screenkey, sxiv, xdotool, xscast, xsnap, zenity, to randomly name a few.