DISCLAIMER: FLIF development has stopped since FLIF is superceded by FUIF and then again by JPEG XL, which is based on a combination of Pik and FUIF. A royalty-free and open source reference implementation of JPEG XL is available on GitLab. See the original notice here: https://github.com/FLIF-hub/FLIF/blob/master/README.md
FLIF is a lossless image format based on MANIAC compression. MANIAC (Meta-Adaptive Near-zero Integer Arithmetic Coding) is a variant of CABAC (context-adaptive binary arithmetic coding), where the contexts are nodes of decision trees which are dynamically learned at encode time.