Leave the Web Player open on your screen. When nobody has touched the mouse, keyboard or screen for a few minutes, it fills the screen with fractals. Move the mouse or press a key to come back.
The Web Player watches for inactivity while its page is open and visible, so keep it in a browser window or install it as an app. For a screensaver that starts by itself anytime, even with every window closed, download the Windows app. The Mac app is coming soon.