MegaZine 3 is a powerful pageflip/flashbook engine, written completely in AS3. It boasts many features, ranging from dynamic page loading to a fully integrated zoom and gallery mode. For a more in-depth listing of capabilities see the features section.
What is this?
MegaZine 3 is a pageflip engine. There are many like it, but this one is… free. And open source, too. This means two things, basically: you don't have to pay for it, and you can even modify it in any way you see fit.
That said, if you use it commercially, you are strongly encouraged to donate! Of course, feel free to donate if you're not using it commercially, too. 😉