kont.txt is a decision tree based legal expert system, and a tool for legal education. It lets you define legal words as terms within a context of other terms, and test the validity of your understanding by providing an 'expert'-system like interview based on your definitions.
I use it to teach law.
You can download the deployed installable windows version at:
This also contains all the sources, documentation and sample knowledge bases.
A (slightly outdated) English documentation is available at:
And a (slightly outdated) German documentation at: