Microsoft Silverlight is a free web-browser plug-in that enables interactive media experiences, rich business applications and immersive mobile apps.
Windows? Check. Mac? Check. Linux? Check. Silverlight works on all major OS's plus all major browsers, including Firefox, Google Chrome, Safari, and yes, Internet Explorer.
Microsoft Silverlight is an application framework for writing and running rich Internet applications, with features and purposes similar to those of Adobe Flash. The run-time environment for Silverlight is available as a plug-in for web browsers running under Microsoft Windows and Mac OS X. While early versions of Silverlight focused on streaming media, current versions support multimedia, graphics, and animation, and give developers support for CLI languages and development tools.
Silverlight is also one of the two application development platforms for Windows Phone, but Silverlight-enabled web pages cannot run on Internet Explorer for Windows Phone as there is no plugin