SproutCore is an open-source platform for building fast rich cloud applications on the web. Specifically, the tools we develop are suitable for building large-scale applications that scale to many millions of users across many different devices.
Given that between smart phones, laptops, netbooks, phones, etc. the one thing all of these devices have in common is that they can run a web browser. It only makes sense that the best, most cost effective way for people to access their data on these devices will be through the web. To truly compete with the native software written for these platforms, however, developers need a way to easily leverage the power of the modern web browser to deliver a compelling, rich user experience.
On the desktop, developers have a pile of build tools, frameworks, and interface designer IDEs to help them create rich dynamic UIs. We need the same thing on the web. That is why SproutCore exists.