For those who've never heard of the author, Matt Mahoney is the author of a number of compression algorithms (and implementations), including the famous PAQ fam

For those who've never heard of the author, Matt Mahoney is the author of a number of compression algorithms (and implementations), including the famous PAQ family of arithmetic coding / context modeling compressors. PAQ and its (many) derivatives are still among the strongest available compressors to date (meaning that they compress very, very well — in general much more than popular compressors like 7-Zip or UHArc), while not being practical due to their incredible slowness.