This is interesting. I'm wondering, since your license says "no derivative works", what exactly am I allowed to do?

If I wanted to start my own pool and needed to change some parts of PoolServerJ (and let's assume I can't do this with a plugin, so I actually need to change YOUR code), this seems to be a "derivative work". Can I do this? I don't think so. Or maybe it's just forbidden to share my derivate work with others?