The range encoder is a fast multisymbol entropy coder (similar to arithmetic coding) with GNU general public license (other licenses on request). Its compression is within 0.01% of arithmetic coding. It is based on an article dated 1979, so it is believed to be patent free. This page includes a PS format paper by G.N.N Martin describing the range encoder.

http://www.compressconsult.com/rangecoder/