After a good number of years, we noticed that there wasn't a "non-patched"
version of a csharp-mode for Emacs. There were a few, but most of them had
comments that they were "in progress" or "about to merge", but then we noticed
that those notices were there even after a couple of months.
Then, we saw a request for a csharp-mode on the cc-mode Emacs site, so we
decided to follow the rules and create one that required no patching or
modification to the core cc-mode engine (which is a good thing). So, this is
the C# mode.