StrmCkr, I've only taken a cursory look at the code and have some mixed feelings about it. I have to agree that it was not made for other people to maintain and extend. It's doable but not straight-forward. While the functionality is impressive (and I do lift my hat for that), and replicating it from scratch would be a daunting task (I'm not claiming I could even do it in any reasonable time-frame), I can't say I'm as impressed with the architecture and some coding practices. Then again, I understand that when one is coding such a project alone, it's tempting to just get things done quickly without worrying about the architecture too much. If others were to participate, it would clearly benefit from some refactoring.
Some of the classes and methods are huge, which makes it pretty hard to see the big picture. I'd prefer smaller and more easily digestible elements with a more hierarchical package structure and delegation. Also, few object-oriented features are used, which makes it seem quite procedural (some might prefer that, though). Most of the low-level code seems pretty understandable and uses English, but I did see some German there too, which might complicate things a bit (didn't seem like a huge problem).