DocBookLite is used by O'Reilly to format its books. It is also used by the subversion project
From "Using DocBook Lite":
Originally, we used the full DocBook application maintained by the OASIS SGML/XML standards group, but have since refined it to a small subset with its own DTD. It has a few additions for some types of books, but mostly the markup should be compatible with the full DocBook.
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Can be obtained from here: ftp://ftp.ora.com/pub/dblite/dblite.tar.gz
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