With the release of the Silverlight 5 framework, I also upgraded the Silverlight Multi File Uploader to version 5. There's no new functionality in this release of the Multi File Uploader, it's the same as v4.3

You can download this release on CodePlex:
http://slfileupload.codeplex.com/

Or use one of the NuGet packages:
http://www.nuget.org/List/Packages/mpost.slmfu
http://www.nuget.org/List/Packages/mpost.slmfu.examples (examples included)

The Silverlight Multi File Uploader is a free and open source Silverlight 5 application. It can be used to upload multiple files simultaneously to your website. It also includes a JavaScript interface and supports PHP.

More info and documentation can be found here.
http://www.michielpost.nl/Silverlight/MultiFileUploader/