I have no idea how long this project has existed but Opera developers have their own showcase site running interesting web apps powered by latest web technologies.
Unlike Apple and Google, these web apps are not optimized for any specific browser. These would work on any browser that supports the relevant technologies.
Opera developers had this in the site’s description:
Shiny Demos is a growing set of demos of the latest Open Web Standards, made by the Opera developer relations team. No browser is blocked: any browser that supports the standard sees the shiny!