Its MIT licensed. And yeah something like that.

ASP.NET is fully supported also in .NET Core.

.NET is not a language, it's a runtime that has a standard library. C# is possibly one of, if not the best, modern programming language. Huge parts of .NET are now OSS. Just yesterday I was looking at the internals of how the List<T> type works in their Github repo.

Edit: Also I'm guessing your talking about Voat which uses ASP.NET. Hands down best web framework I've ever used.