http://gale.org/ is a primary resource.  The install.xml file in this
directory (build instructions) are from there.

See also:

http://old.gale.org/
http://www.epinions.com/cmd-review-249C-1248C017-38852C92-prod1  
   (good description)
http://www.cs.washington.edu/homes/tlau/gale/
http://www.cs.cmu.edu/~visigoth/gale.html
http://download.gale.org/
http://www.slackers.net/gale/
http://www.ugcs.caltech.edu/~jtr/gale/
http://www.cs.washington.edu/homes/tlau/gale-announce


Required or accessory software:
ftp://ftp.chiark.greenend.org.uk/users/ian/adns/
http://www.hpl.hp.com/personal/Hans_Boehm/gc/
You will also need the Gale tarball (of course) and the RSAREF 2.0 source
code, both available here.