It's important to remember that C# does not imply .NET
Xamarin has done some great stuff lately, for example you can use C# to make a native 3-platform mobile app. This is still proprietary tech, but it isn't Microsoft and it isn't .NET
In my eyes the best thing about the .NET ecosystem is the tools, if you like me fancy a polished IDE like IDEA, then VS is definitely one of the best ones around. In my eyes tools are more important than platforms, languages and licenses. The productivity hit of poor tools is much more expensive than anything else.
Also, if you are looking at C#, don't forget to consider F#.
Compare a minimalist service built on Node/AWS with one built on F#/Azure and it's not too different in cost but a much nicer language and better tools.
This has changed a lot, especially over the last couple of years, a lot due to the F# project.
You should look at self-hosted NancyFx or ServiceStack with F# as a good alternative to Node.js
The fact that the "other solutions" aren't popular is probably just because C# is the go to language in windows/.NET shops that already have knowledge and infrastructure. It's not that they are technically inferior.
Xamarin has done some great stuff lately, for example you can use C# to make a native 3-platform mobile app. This is still proprietary tech, but it isn't Microsoft and it isn't .NET
In my eyes the best thing about the .NET ecosystem is the tools, if you like me fancy a polished IDE like IDEA, then VS is definitely one of the best ones around. In my eyes tools are more important than platforms, languages and licenses. The productivity hit of poor tools is much more expensive than anything else.
Also, if you are looking at C#, don't forget to consider F#.
Compare a minimalist service built on Node/AWS with one built on F#/Azure and it's not too different in cost but a much nicer language and better tools.