Moonlight is an open source version of Microsoft Silverlight for the Linux platform. Version 1.0 is ready for Linux now. It is licensed under the GNU GPL. The release was delayed for the latter part of 2008.

Microsoft apparently did provide some assistance to Moonlight. They gave technical guidance. They also provided the Silverlight unit tests to help ensure that Moonlight was an accurate emulation. Finally, Microsoft opened up some of the Silverlight 2 code as open source.

Silverlight 2 is already out from Microsoft. Expect there to be a Moonlight 2 to complement the Silverlight 2 platform. Hopefully with further assistance from Microsoft, Moonlight 2 will be released in a timely fashion.