The name is confusing. A C shell already exists (http://en.wikipedia.org/wiki/C_shell). An alternative name could be CSharpShell. Btw, while googling that name, I found CsharpRepl, which seems to be a somewhat similar tool.
For example, I make use of both ipython and bpython, both of which I refer to as either shells or REPLs; though neither program is a proper shell (in the /bin/chsh sense), and though people also call them “interpreters” (technically, the python interpreter still interprets), “environments” (vague) or even “IDEs” (wat?) – the concept behind the tools is popular and well-understood.
Personally I think it’s particularly funny to call these Enhanced REPL Shell Interpreter Environments (or what have you) “IDEs” and lump them in with Eclipse or Visual Studio or those other behemoth coding tools; I like bpython and ipython for the myriad ways they are un-Eclipse-y, and if I did C# I would presumably get into CSharp for the same reasons. All of which, like many bicycle-shed innovations, are mere matters of taste.