TidBITS:

One of the best features of the Apple TV is its Aerial screen saver. That’s not hyperbole—Apple always makes a big deal out of the new scenes it adds to tvOS, often promoting them as a marquee feature of major tvOS updates. If you have liked these screen savers on your TV, you can get them on your Mac, thanks to the free and open-source app Aerial.

I’m not sure how the development team gets away with it (Aerial is currently maintained by Guillaume Louel), but Aerial has been available for five years without interference from Apple. Which is a good thing!

Many of these screen savers are spectacularly beautiful.