google/brotli · GitHub

https://github.com/google/brotli/

Brotli is a generic-purpose lossless compression algorithm that compresses data using a combination of a modern variant of the LZ77 algorithm, Huffman coding and 2nd order context modeling, with a compression ratio comparable to the best currently available general-purpose compression methods. It is similar in speed with deflate but offers more dense compression.

Google Open Source Blog: Introducing Brotli: a new compression algorithm for the internet

http://google-opensource.blogspot.jp/2015/09/introducing-brotli-new-compression.html

While Zopfli is Deflate-compatible, Brotli is a whole new data format. This new format allows us to get 20–26% higher compression ratios over Zopfli.