A year ago Ian Lackey and I decided to create a DotNetNuke site that allowed users to upload .Mp3 files and play them using Silverlight visualizations. We planned to expand the site and to make a SDK so that people can create their own visualizations. However, we became busy with our latest DotNetNuke book, and other projects, and we never got around to making the enhancements.
We decided to publish the source code for the site as Open Source, because… well… we can 
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By using DotNetNuke for the site, we did not have to put that much work into it, and other than registering the domain name, and buying a skin, we put no money into the site. When you use DotNetNuke as the base for your website, you do not have to create the majority of your site. Things like the look and feel (you can simply buy a skin), page management, menus, user registration, password recovery, security, roles, permissions, error logging, are all created for you. Using the directions such as the tutorials I have published at: DotNetNuke® Module Development Help Website, you can quickly create the custom functionality you need.
For Silverlight and DotNetNuke code, you can find plenty of free code an examples at: http://dnnsilverlight.adefwebserver.com/
You can download all the custom code and modules for MyStudioServer.com and adapt it for your own uses at:
http://mystudioserver.codeplex.com/
This blog post is cross-posted from my personal blog site (http://openlightgroup.net/Blog/tabid/58/EntryId/155/MyStudioServer-goes-Open-Source.aspx).