For example, you can say, take a true-color animated WebP, quantize it to 64 colors max, but make sure the first 16 colors is the same as the default VGA palette, then save the result as an animated GIF.

There's no point in example images, because the power of this tool is, you have full control on specifying how the conversion should be done. Just quantize to 256 individual colors? Sure. Convert to web-safe palette? Got you covered. Limit the colors to 8 for each 4 x 4 pixel blocks? Smooth sailing.

Full disclosure: it generates much better results than Imagemagick "png8:", and it handles animated PNGs too.