Appendix A contains outtakes from the text of the novel -- places where explanations got technical enough to bog down the story and had to be trimmed back.
Appendix B contains a glossary.
Appendix C is a partial compilation of my more coherent notes from the development phase.
There is an Appendix D as well, but it has to do with character issues rather than technical ones. It also contains plot spoilers, so is not included here.