FOP is the world's first print formatter driven by XSL formatting
objects. It is a Java application that reads a formatting object
tree conforming to the XSL candidate release (21. November 2000) and 
then turns it into a PDF document or allows you to preview it 
directly on screen. 
    
FOP is part of Apache's XML project. The homepage of FOP is 

WWW: http://xml.apache.org/fop/
