Earlier this week, Microsoft announced the Silverlight product name. Silverlight is a micro-framework for developing client web applications, in particular web media applications. A micro-framework is a platform that trades off having a comprehensive set of features so that it can have a limited size for distribution and deployment. There have been similar examples of these kinds of micro-frameworks in the past, such as for mobile devices, cell phones, and even watches. The Silverlight niche is to fit into the space of web browser plug-ins. This is an interesting space because you generally have a lot more system resources available than for something like a cell phone, but you can't make users install an enormous download first like the full framework.
Tim Sneath has a list of trivia up about the release although you'll have to wait until MIX to see that last announcement. I won't have too much to say about Silverlight as I didn't work on it past its very early development.