For the last three weeks, a decentralized group of Mono developers has been hacking together an implementation of Silverlight for Linux. Project lead Miguel de Icaza chronicles the process on his blog, calling the weeks of 12-hour-plus days "the most intense hacking days that I have ever had."
The result is called Moonlight. There’s no package installer yet, but Miguel will be presenting a demo for Linux at ReMix07, the traveling Microsoft event landing Thursday in Paris. He has some nice screenshots on his site, as well as details about what still needs to be done and how to get involved.
Mono (the thing that made Moonlight possible) is an open source set of software tools for .NET developers to port their apps to multiple platforms like Linux and Mac OS X.