Mobile Developer's Guide To The Galaxy, 13th edition

The free, community driven handbook about mobile technologies: Over 20 experts from all over the world are sharing their know-how on topics like mobile app design, platform-specific aspects of app development, cross-platform development, mobile analytics, accessibility, monetization, app stores, LBS, NFC, app testing and a lot more.
The book is popular among developers wanting to deepen their knowledge and decision-makers planning to enter the mobile business alike. The content gets updates and extended continuously, 13 editions have been published since 2009 and 50,000 hardcopies have been distributed.
Enough Software, a mobile development agency from Bremen, Germany coordinates the project and also offers the book as a free hardcopy or pdf available on their website: http://www.enough.de