The download includes the D* executable and full source code for the following: basic D* programming examples, Lagrangian dynamics, and a basic interactive geometric modeling tool. This is unsupported code but if you find bugs or have feature requests send an email to firstname.lastname@example.org.
There is a book that describes the dynamics algorithms, as well as simple procedural modeling techniques. You will probably want the book if you are downloading the code, since it has more detailed documentation of the software than is available in the download. You can get the book here: Symbolic Dynamics and Geometry: Using D* in Graphics and Game Programming