The .NET framework is popular in corporate environments. We also believe this is the perfect tool for startups and hobbyists.
You can create portable code that functions across iOS, Android, Windows tablets/phones, desktops, servers and embedded devices, for free.
Everything from the compiler to the core runtime is open source.
The BizSpark program allows any startup to get all Microsoft tools, including $150/month of Azure service, for free.
Visual Studio Community 2015 is a professional grade IDE that you can use freely as a hobbyist.
C# is closely related to Java and C++. As such, it can be easily read by a big base of developers.
Nicolas Dorier, created the most popular Bitcoin Framework for .NET, called NBitcoin.
Every person I met who learned about C# will tell you it is the best language out there, even if it is not the one they are using at the moment.