Really? Why do Oracle claim ownership of the code and even the api to company like Google? Threatering everyone who implement their variant of Java?
On the other hand most of the C# library have been release the source code and the language is itself fully approved by EMCA and ISO (check wikipedia for reference), something Java is not (Because Java lacks any formal standardization recognized by Ecma International, ISO/IEC, ANSI, or other third-party standards organization, the Oracle implementation is the de facto standard.). .NET doesn't run only on Windows, Mono is project that exist for a while and it's use in many context. You can developer even application for Andriod phone in C#, because the language is open, you are welcome to make a compiler and re-use it everywhere!