I am honored to be a co-author and editor-in-chief of the most
comprehensive, detailed, and complete guide on matters related to compliance
of copyleft software licenses such as the GPL.
This book, Copyleft and the GNU
General Public License: A Comprehensive Tutorial and Guide (which we
often call the Copyleft Guide for short) is 155 pages filled
with useful material to help everyone understand copyleft licenses for
software, how they work, and how to comply with them properly. It is the
only document to fully incorporate esoteric material such as the FSF's famous
GPLv3 rationale documents directly alongside practical advice, such as
the pristine example,
which is the only freely published compliance analysis of a real product on
the market. The document explains in great detail how that product
manufacturer made good choices to comply with the GPL. The reader learns by
both real-world example as well as abstract explanation.