Microsoft Silverlight 4.0.60129.0 version

Silverlight is a powerful development platform for creating engaging, interactive user experiences for Web, desktop, and mobile applications when online or offline. Silverlight is a free plug-in powered by the .NET framework that is compatible across multiple browsers, devices and operating systems to bring a new level of interactivity wherever the Web works. With support for advanced data integration, multithreading, HD video using IIS Smooth Streaming, and built in content protection, Silverlight enables online and offline applications for a broad range of business and consumer scenarios. All Silverlight runtimes support rich media capabilities and enable fast, cost-effective delivery of high-quality audio and video to all major browsers including Firefox, Safari, Internet Explorer (and new in Silverlight 4) Google Chrome running on the Mac or on Windows. The designer experience remains largely the same for all runtimes as well. The main difference resides in the developer experience.
The download link takes you to the Windows version, while you can download the 13.3 MB Mac version from here.