For fast image processing, Fnk uses the Pixel Bender technology used by Adobe on their graphical applications such as After Effects (and others, in the future). This is a shader-like language that is based on GLSL, so shader programmers will feel right at home.
Any Pixel Bender filter can be used inside Fnk, so using Adobe’s Pixel Bender gallery is the best way to find and share filters online.
Additionally, filter programmers may be interested in getting the (also free) Pixel Bender Toolkit. This toolkit allows anyone to quickly develop and test new filters before they’re used inside of Fnk, or any other Adobe application (remember to turn on the “Build” > “Turn on Flash Warnings and Errors” option if you want to compile a filter that you intend to run inside Fnk, though).