Playing around with gcj the other day, I noticed fop is not gcj-"compatible" (yet) due to its AWT renderer that requires swing classes. Not having studied the redesign code in detail, I'd like to propose (if not already part of the master plan) to source out the renderers in small modules so that not only limitations in the Java VM can be avoided :-) but also to follow the KISS principle when your use case only requires PDF (or RTF or ...) output. Another idea (from a "./configure && make install" background) would be to have "options" "--enable-pdf", "--enable-ps", "--enable-rtf" & Co. to the build process that determine which renderers are to be included.
GNU Classpath has AWT/Swing today. This should no longer be a problem. Other dependencies that GNU Classpath might not have have been removed, too. Some people have reported that FOP works with GCJ but to what extent is unknown at the moment. Please reopen if any problems remain. Generally, the renderers are already pluggable and can be selectively removed from fop.jar by hand if necessary. Registration happens through the JAR Services mechanism (see META-INF/services/*).
batch transition pre-FOP1.0 resolved+fixed bugs to closed+fixed