You might already be aware of this but it was the first time I've come across this so I thought I'd let you know. I haven't looked at it too closely but I thought that it might be able to replace the JTS for enhanced polygon support. It says api but I think it's a stand alone library that doesn't require ESRI. The best part is it's APL 2.0 licensed.
Thanks, Zach, we'll definitely take a look!