I have published the following books:

20 Years of KDE: Past, Present and Future

This book presents 37 stories about the technical, social and cultural aspects that shaped the way the KDE Community operates today. It has been written as part of the 20th anniversary of KDE. From community founders and veterans to newcomers, with insights from different points of view, the book takes you on a trip through the history of one of the buggest Free Software communities. You can find out more about it at 20years.kde.org/book.

Open Advice
It is a collection of essays by 42 prominent Free Software contributors. It answers the question what each of them would have liked to know when they started contributing to Free Software. You can find out more about it at open-advice.org.

I have contributed chapters to the following books:

ABC des Freien Wissens
It is a collection of essays about different topics related to Open Knowledge. You can find out more about it at Wikimedia Deutschland.

Qualität in der Inhaltserschließung
It is a collection of texts about the various aspects of quality in subject cataloging. You can find out more about it at De Gruyter.

Leveraging Wikipedia: Connecting Communities of Knowledge
It is a collection of essays from various people across the library sector and the Wikimedia Movement focusing on how these two communities can collaborate and flourish together. You can find out more about it at the ALA.