I don't see the point of a Flash alternative. Emulating a proprietary format is never going to produce results that compare to the original in terms of functionality and performance. And frankly, the open source community would have to make a considerable mess of the Linux kernel for it to be considered a "Windows alternative."
What I would like to see is not the development of open source versions of proprietary technologies, but the eradication of proprietary technologies entirely from general website implementations. It's 2010 and I still see websites designed entirely for IE, or entirely in Flash, and I have to wonder who hired the morons that developed them. I won't even use any site that insists I install Java. Hopefully HTML5 will help in this regard, even if it is a long ways off.