Further evidence of Microsoft's growing commitment towards interoperability and open source -- the ASP.NET MVC source code has been released under the Microsoft Public License (MS-PL).
ASP.NET MVC 1.0 was officially released at MIX09 a couple of weeks ago. It provided developers with an alternative to developing ASP.NET applications using Web Forms. The Model-View-Controller approach is designed for tighter control over the application and provides the ability for Test Driven Development (TDD).
Haven't heard of the MS-PL? It is an OSI-approved open source license. According to Scott Guthrie's blog, the MS-PL license means "no platform restrictions and provides broad rights to modify and redistribute the source code".
Microsoft has also made SharePoint Designer 2007 free to download. It's not open source, but it's another step to demonstrating their desire to have developers work on their systems and to open doors to the greater open source community.
Can't wait to see what they do next.