Thanks all for the suggestions. Here's some that I've tried:
libdither - https://github.com/robertkist/libdither currently only a library but a cli tool is said to be in development
Dither Guy - https://github.com/manoelpiovesan/dither-guy inspired by Dither Boy. Has stalled a few times when working with big images but good otherwise
Ditherista - https://github.com/robertkist/ditherista - most amount of dithering options and a nice gui
didder - https://github.com/makew0rld/didder really like this one, great for batch processing
onebitdithertool - https://github.com/timheigames/onebitdithertool not updated in a while but has a few options for saling and dithering. Maybe go for Dither Guy or Ditherista if you want a native gui
