JCALG1 is a small, open-source, LZSS derived compression library.

• Features Coded in 100% 32bit x86 assembly language for maximum performance and minimum size.
• Good compression ratio, typically much better than ZIP’s deflate.
• Extremely small and fast decompressor.
• Adjustable window size to allow for faster compression at the cost of compression ratio.
• Decompression requires no memory, other than the destination buffer.
• Easy integration with any application.
• Free!

http://www.collakesoftware.com/jcalg1.htm