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.
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.