Microsoft Silverlight was a flash-like player developed by Microsoft in 2007. It was originally made Microsoft's own flash-like runtime, even going so far as to garnering a little over two thirds of it's market share by May 2011. However, after this peak, Silverlight's popularity quickly depreciated. Silverlight used XAML (Extension Application Markup Language), as opposed to Adobe's ActionScript. Silverlight, with it's first version being developed in 2007, follows the design behind Windows Vista/Windows 7 (which was in development at the time), with an aero/aurora theme to it.
Silverlight's compatibility was amazing; since Microsoft originally developed Silverlight, Silverlight was able to achieve support for multiple audio codecs and video codecs, all without Windows Media Player. This behaviour was the same across multiple OSes/platforms, these being Windows, macOS, Windows Mobile, and Symbian phones/platforms. Unfortunately, it wasn't available on iOS or Android.
Before it's death in late 2021 (last version in early 2019), and deprecation for HTML5 in Windows 8 (2012), Silverlight was actually used to cover/stream over several platforms. Some examples of this occurring would be with the NBC coverage of the 2008 Summer Olympics, the 2010 Winter Olympics, even Amazon Video and Netflix who used it for their instant video streaming services. Silverlight was also made before CSS got it's grid and flexbox displays, which did make it difficult to make rich, large, and good looking programs. Silverlight's versions were released nearly annually; with Silverlight 1 being released in 2007, Silverlight 2 in 2008, Silverlight 3 in mid 2009, Silverlight 4 in late 2009, and finally, Silverlight 5, with it being released on December 9th, 2011. Silverlight's doom was also rumored in 2011, which is also the year that Silverlight 5 released.
If you still want to experience Silverlight/XAML related apps, you can do so at Open Silver.