Raymond yee’s book on Web 2.0 and mashups is available online at his blog. Currently all the chapters are available as PDF files at this page. He had released the book under creative commons license.
Getting Started with Web 2.0 February 10, 2006
The buzz word of year 2005 was Web 2.0, which marked release of whole new spectrum of web applications with rich user experience. Web 2.0 had transformed the conventional web (web page) into dynamic applications updated in real time based on streaming xml data. Many of these rich internet applications (RIA) were evenchallenging their desktop counterparts. And it made a paradigm shift in making web as a platform for running real applications.
Another important aspect of Web 2.0 is open standards. It encourages and in times even mandates open protocols, APIs to share information over services along with web pages. And it enables public consumption of information by others eg: mash-ups.
Though technologies and patterns got pronounced more in synonym with Web 2.0, I strongly believe that the power of Web 2.0 is social computing. It inherently supports community building through open communication and improved collaboration. And showcase the power of collective intelligence.
Among hundreds of startup companies, Yahoo, Google and Microsoft were leading this revolution from front. IBM had recently joined the wagon with open Ajax effort
Visualizing Web 2.0 February 10, 2006
Dion Hinchcliffe presented a consolidated, simple overview of web 2.0 technologies stack. Worth watching at it.

What is Web 2.0 application? February 7, 2006
Despite availability of materials in plenty on web, I haven’t come across a simple, precise definition for Web 2.0.
Here is my definition
“Any web application designed to support communication, collaboration, collective intelligence and social interaction between people could be categorized as a Web 2.0 application”.