XMill: The XML Compressor

This popular tool was developed by Hartmut Liefke and myself in the Summer of 1999 at AT&T Labs. The official XMill website with the original software is still there, and holds version 0.7. More recent developments:

A version that supports the binary format of XMLTK is here. It was developed by an undergraduate student at UW.
An extension (version 0.8) was developed by Hedzer Westra in 2003. Supposed to be available here (doesn't work for me, though).
An update (version 0.9) by Ben Colver in 2004: here is the tar file. Tested:
GCC 3.x
NetBSD 1.6ZK, HP-UX 11.11, SunOS 5.8
GNU Make, BSD Make, and the make that come on HP-UX and SunOS.
libz, libbz, libbz2, xmill builtin libz, xmill builtin libbz
(not on Windows)
And another update (version 0.9.1) by Ben Colver in 2004 is here. This has been modified to build with GCC 2.95.3 and with GCC on Windows (mingw).