I know, so exciting, a license.
We are dual-licensing under this uber-liberal license because:
We are changing the license to allow parts of the compiler to be reused as part of MonoDevelop, our LINQ class libraries and to embed it in ASP.NET.
In MonoDevelop: This will allow the compiler to be used to improve code-completion to support C# 3.0 as well as improving the heuristics when offering completions. This will reuse the front end and parts of the backend.
Compiler hosting inside ASP.NET: This will embed the whole compiler into the ASP.NET process, eliminating about one second for each compilation of a piece of code. In the past, for each request for an uncompiled resource, we would have to call the compiler, wait for its output and then load the output. This typically shaves between 0.7 to 1 second on those scenarios, ideal to improve the developer experience.
LINQ Class Libraries: This will allow us to reuse parts of the compiler in our System.Core implementation for LINQ for the current 3.5 generation and upcoming generations. Many corner cases are handled by the compiler, and we will now be able to lift those pieces. This will mostly use the backend of the compiler.