Apache FOP is maintained and has only recently reached version 1.0 but don't be fooled this isn't the first release as is the culmination of many years of work. There was a period several years ago where it looked as if the project was dead but they were working on major changes at the time. Since then there have been releases on a regular basis with each one improving the compatibility and functionality.
Also and if you do have problems (I mean bugs or technical issues with the renderer not questions about FO) I've found the FOP team really helpful and have always given quick responses.
