[Dwedit]

FLIF got integrated in to JPEG-XL as the modular mode.

[F3nd0]

If I recall correctly, that's FUIF, originally created by the same author as FLIF's successor of sorts.

[JyrkiAlakuijala]

Not really. FLIF is too slow to decode, about 20x slower than WebP lossless. JPEG XL modular mode uses a similar static context modeling with WebP lossless and Brotli and likely LZHAM where all the entropy codes are generated at decoding time. Also JPEG XL forces tiled coding, making multi-threaded decoding a possibility.