Moonlight is an open source implementation of Silverlight, primarily for Linux and other Unix/X11 based operating systems. The last Moonlight release (Moonlight 4 Preview 1) provides support for most features of Silverlight 3, as well as compatibility with Silverlight 4. The Mono project does not provide binary downloads for Moonlight; however, packages for most Linux distributions can be found online, either in official distro package repositories, or provided by popular third-party repositories.
Note: Moonlight isn’t actively developed anymore. If you’re feeling adventurous you can probably get it working by compiling from source, but we recommend you move away from Moonlight as soon as possible.