Wikipedia
AdvanceCOMP
AdvanceCOMP is a set of cross-platform command line data (re-)compression tools. The utilities allow modifying an already-compressed file, with the intent of reducing the file-size by optimising the compressed representation. The AdvanceCOMP suite is freely available under the terms of the GPLv3 license.
AdvanceCOMP works with files using the LZ/ Huffman-based compression algorithm known as DEFLATE, the most widely used compression encoding systems in use. A large number of file-formats include DEFLATE as part of their specification, most notably PNG, gzip and ZIP.