What I did was edit the Wikipedia articles through heavy or light rewriting, depending on what I figured the article would need to look good in book form. I then went to find additional information from other sources where I felt having more could be fun, and I added screenshots. And then I conducted interviews with many people who were involved in producing the classic graphic adventures. I interviewed creators like Al Lowe of Leisure Suit Larry, Lucasfilm’s David Fox, and Michael Bywater, who worked with Douglas Adams on the game Starship Titanic. The book took much longer than expected… the original idea after all was to merely compile an encyclopedia from Wikipedia, a book for perhaps a small but dedicated group of fans like me. But after sending myself the first draft version, I realized much more editing was needed to have something really fun.
What a great way to write a book. Philipp Lenssen says he is donating 50% of the book’s revenues to the Wikimedia Foundation, but doesn’t mention whether he contributed any of his original findings back to Wikipedia (although now I think about it, I’m fairly certain Wikipedia discourages original research).
He’s released it under the GNU Free Documentation License, and you can download the HTML documents in a .zip file.