Use, study and develop advanced digital halftoning algorithms with Halftone Laboratory, a GIMP plug-in backed by a highly modular and extensible library. It uses .NET/Mono and GIMP#.
GIMP plugin - dynamic filters
GIMP plugin - spot functions
GIMP plugin - adaptive SFC clustering
GIMP plugin - presets
Example artistic dither: modified screen
Example artistic dither: Verovka-Buchanan + JaJuni + swirls