This is the final part of this book; if you're still reading, you weren't scared by the term Appendix. Appendices are often seen as something with minor importance or somehow collateral to the main topics of the book. Also, its location at the end of the book doesn't help much to attract readers.

Anyway, because you are the kind of reader that starts from page number one and goes on through each chapter or just because you read the introduction and recognized yourself as a member of the ESRI community, we're going to have explore in the borderline land that crosses the proprietary and open source software.