Earlier this month Novell quietly released Moonlight -- a Linux client for Microsoft's Silverlight technology. Silverlight is a .Net-based cross-browser, cross-platform plugin for delivering rich media to the Internet. In a nutshell, it is Microsoft's version of Adobe Flash.
To use Moonlight you need to make sure you have all of the current Mono packages installed. Ubuntu and Fedora come ready out of the box. On other distributions, check the package manager. You can also compile Mono from source.
Moonlight functions as a Firefox plugin -- but don't try it with Firefox 3, because support for that version of the browser is buggy, according to the developers. To install it, visit the Moonlight Web site with Firefox and click the appropriate button for your hardware platform to launch the install dialog. If you don't see the dialog, Firefox has more than likely blocked the installation, and a yellow bar will appear at the top of the screen. You have to click the Options button on the bar and add the domain to the allowed sites in order to lift the block. Once that is done, click the button again to open the Software Installation dialog, click Install Now, and restart Firefox to finish the process.
The Moonlight wiki lists sites you can visit to test the plugin. Weihong Hendricks' Asset Allocator is a nice example. It is an interactive graph for calculating asset risk. It displays grab bars that allow you to change the allocation values; as the values change, the graph is updated in real time.
The binary version of Moonlight does not have audio and video support built-in. If you want the audio and video features you have to build Moonlight from source using the instructions on the Mono wiki.
The Moonlight team has already started working on support for Silverlight 2.0. For the adventurous, there is already an alpha release.
There is a fierce debate brewing about the use of Moonlight and Mono on open systems such as Linux. Microsoft has granted users the ability to use the software without fear of litigation through their collaboration deal with Novell. Some users are fine with this, some are not.
No matter the licensing, without Moonlight, Linux users will be locked out of sites that utilize Silverlight, similar to the way things used to be with Flash -- and Silverlight appears to be here to stay, for better or for worse.