Their marketing: "Famo.us provides a powerful JavaScript framework and developer tools designed to build rich, fast web applications." Yeah, it looks like it's mainly targeted toward mobile devices, not that it was clear before today. Earlier reports mentioned desktops together with mobile, like this one:
http://techcrunch.com/2012/09/10/famo-us-is-a-gaming-engine-...
"...it works on nearly any platform, including desktops, Android, and iOS."