From the page on An Introduction to Seaside:
Seaside is a Web development framework implemented in Smalltalk. It allows the easy creation of powerful Web applications using high level abstractions on the application components and on the underlying hypertext transfer protocol.
While I have not read this book, I did take a dive into Squeak Smalltalk and heard a wonderful 4 hour presentation on Seaside by Avi Bryant. Seaside takes a novel approach to web application development that looks quite fun.
This book looks like a great read!