Microsoft has released a "shared-source" version of the DotNet CommonLanguageInfrastructure, code-named Rotor. Rotor will build and run on WindowsXp, FreeBsd, and MacOsx. It contains source for implementations of the CommonLanguageRuntime, CsharpLanguage and JScript compilers, development/build tools, documentation, sample code, and test suites.
The shared-source license prohibits commercial use. It does allow use for academic and research purposes, or for personal experimentation. It allows modification and redistribution for non-commercial purposes.
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Clearly this is paranoid... and yet....
Microsoft sues Mono or DotGnu (or some large corporation using Mono or DotGnu) claiming that Mono or DotGnu "stole" something from the SharedSourceCli. So a corporation that wanted to use DotGnu would be legally cornered into complying with the Rotor licensing, which pretty much means they couldn't use it. And like most corporations, they'd stand way back anyway just because lawyers are starting to get involved.
So then the SharedSourceCli serves the purpose of impeding adoption of less restrictively-licensed open-source implementations.