This is a new zlib encoder (compatible with existing zlib decoders) that does a few percent better than gzip -9 at the cost of 100x more CPU time. Instead of the obscure name Zopfli I think “gzip –11” would be a good mnemonic, as in ours goes to eleven.
Originally shared by Abraham Williams
http://googledevelopers.blogspot.com/2013/02/compress-data-more-densely-with-zopfli.html