"Welcome to the Wikibook Online Work (WOW) Projects! This book is a collaborative effort of students from universities in mainland China, Taiwan, Malaysia, and the United States all collaborating during the fall of 2007 on a book titled “Web 2.0 and Emerging Learning Technologies” (also known as the “WELT”)." Anyone is welcome to join them in their efforts here.

This wikibook gives an introduction to Web 2.0 and goes into detail on topics such as Foundations, Learners, Instructional Design, Environments and Tools and the future. It's very informative and well written.