There are a large number of Open Source tools available for Flash, and this book takes the most popular of those and explains how they work and how to fit them into an existing workflow.
Some of these tools are hugely popular, with the most recent version of Papervision3D alone (released in July 07) being downloaded more than 300,000 times and being used in projects for companies such as Nike, Audi, and Le Coq Sportif. This is the only book dedicated to Open Source Flash projects, and is written by the project leads themselves.