heatshrink: An Embedded Data Compression Library

heatshrink: An Embedded Data Compression Library:

released under a BSD license, it can run in very small amounts of memory (under 50 bytes for practical decompression), and it can work in small increments while addressing the other needs of a hard real-time system.
presentation: zip Code: Unpacking Data Compression by Scott Vokes @ InfoQ

A nice introduction how common compression algorithms work