Use arbitrary greyscale image as dithering matrix. Operates the same way as the standard bayer matrix does for ordered dithering.
Allow the user to create their own artistic dither patterns.
Side benefit of also allowing use of other bayer matrix sizes (I like love the dither levels of 2x2 bayer but find the higher dither levels of larger bayer matrices to be rather ugly).
There’s some examples here: https://share.krita.org/p/1106497/
There was an example Krita file for doing HD index painting in Krita which had a whole heap too, but the link to that is dead.
Basically any greyscale image can be used (with varying results), just a matter of thresholding it with the value of the current pixel.