Adobe has FlashPaper, which is what Scribd uses, or used to. I know the owner, so I would have to check with him what they use currently. The FlexPaper link you gave seems that they took FlashPaper and translated it from Flash to Flex. The creators of FlexPaper claim that their stuff is open source, but you have to pay for it? I don’t know, but when I think of open source, I think of free software.
Question - why do you “need” the page turning experience?
From my own experience of using several sites that include that kind of page-turner, it’s been utterly awful to use – slow to load, slow and difficult to navigate, hard to read because of the way the pages move – not to mention that it’s going to be really, really tricky to find something that doesn’t use Flash, let alone something that works on mobiles (if that’s a deal-breaker then you might as well give up now).
The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale. http://www.opensource.org/osd.html [/ot]