I was looking at this kind of stuff recently, but finally did not actually start the project. So these I have not really tried, but they did look among the best free solutions: http://www.flashpageflip.com/FreeFPF.asp ,which his free(has php and asp based pro versions, too) for commercial, but forces a tiny txt url link at bottom left (in some projects this does not really matter) , and this other one, not allowed in commercial projects : http://www.megazine3.de
Besides that, there are many great services that even host for you the pdf and the conversion is automatically made by them, and served.
Depending on bandwidth, time, etc, I'd go for just using a free converter like mentioned, grab the resulting swf files, host the swfs my self, embedding with the typical html tags. Probably would not be much complex to do some scripting in python, or other language, to automate it, if it's a lot of PDFs.
EDIT: Sorry, did not pay attention to the "open source" requirement. Only Megazine, of the mentioned.