Interesting, it seems they're using "LZJB" compression. <a href="http://en.wikipedia.org/wiki/LZJB" rel="nofollow">http://en.wikipedia.org/wiki/LZJB</a><p>I've been on the lookout for a fast compression algorithm that gives reasonable ratios, while having a liberal enough license. LZJB is licensed under the CDDL, which is GPL-incompatible, but it looks simple enough to be re-implemented.