The book details 37signals’ rapid prototyping and web-app development process with the goal of showing you “the smarter, faster, easier way to build a successful web application.”

If you’re familiar with the company’s successful web applications, Backpack and Basecamp, the ebook essentially answers the question, “How’d they do that?”

Designers and studios working with new up-and-coming technology firms will also find the book useful for getting a better understanding of the philosophy and working methods being adopted by many “Web 2.0″ companies.

PDFs of the eBook are still $19, but the HTML version is absolutely free. Yay!

37signals via Lifehack.org