Netvibes, my favorite personalized homepage, is a site that thinks big. There are so many platforms for widgets/gadgets/modules, and each platform uses its own format, so the most popular personalized homepages got the most widgets.
Netvibes has just launched a universal widget API, that should let you develop widgets for Netvibes, Google Personalized Homepage, Windows Vista, Apple Dashboard, Opera etc.
There are some sample widgets here and you'll notice they keep their Netvibes look on other platforms, which is not a good thing. But Netvibes gained a lot of points by inviting developers to build gadgets using their API: their mission is excellent and the number of widgets built for Netvibes will increase.