I have just launched a new project on java.net called shard. It's goal is to be an opensource d20 gaming engine that is small, lightweight and embeddable. There are several d20 applications and tools, but none that can be embedded into other applications or used as a core for pc gaming. In particular, my interest in starting an embeddable d20 engine began when I tried adapting another application to be used as a web based utility application. I won't mention the project that was being used, but the issues were great enough that I decided that the d20 community needed a better option.
One of the first uses I hope to see is to convince the folks at gmgen to use the dice implementation I've put together. It's solid and can handle a wide range of dice uses (multiple rolls, drop high/low rolls, etc). It would be a great boon to our gaming community (both pen/paper and electronic) to have a solid d20 engine. Can you imagine the possibilities of Neverwinter Night quality games if the d20 ruleset was already implemented for their use?
I have posted a wiki for anyone interested to drop ideas/comments.