FOP was the first big open source project I started. Six years ago, I donated it to Apache and shortly after that stopped working on it myself (I didn't have time once I started working at Bowstreet).
It was a lot of fun and I learnt a lot about software craftsmanship.
I still get an email every few weeks asking me a question about using FOP. Not entirely sure why my email address would be easier to find than the mailing list at Apache.