Aurora
Layered curtains of light over a night sky
Green and violet curtains of light hang over a dark sky and drift sideways, brightest along their lower edge and fading out before they reach the top of the frame. Stars show through the gaps and thin out behind the strongest ribbons. Low warp reads as a calm glow, high warp as a solar storm.
Rendering cost: medium. A few dozen samples per pixel: comfortable fullscreen on a discrete GPU, but cap the pixel ratio for a retina hero. How to tune it
Take Aurora with you.
Aurora is free. Sign in and it is yours — the background itself, with your settings already saved in, ready to drop into your site. The account is only somewhere to put the files. No card now, and no card later.
The other 61 come with a licence, $9.99 once.
$0forever
Your preset is in the URL. It survives the trip.