Microsoft has released official download links of SilverLight 4. It is currently available for Windows and Mac OS X system.
Silverlight is a web application framework to create interactive apps integrating multimedia, graphics, animation and video streaming for desktop and cell phones.
Silverlight 4 adds support for data binding, enterprise networking and printing. Nearest match to Microsoft SilverLight is Adobe Flash which is traditional supported by many websites and browser.
SilverLight supports Google Chrome browser, Internet Explorer, Mozilla Firefox and Apple Safari.