F# (pronounced F Sharp) is a multi-paradigm programming language, targeting the .NET Framework, that encompasses functional programming as well as imperative and object-oriented programming disciplines. It is a variant of ML and is largely compatible with the OCaml implementation. F# was initially developed by Don Syme at Microsoft Research but is now being developed at Microsoft Developer Division and is being distributed as a fully supported language in the .NET Framework and Visual Studio as part of Visual Studio 2010.

Code example:
(* print a list of numbers recursively *)
let rec printList lst =
    match lst with
    | [] -> ()
    | h :: t ->
        printf "%d\n" h
        printList t


source: F Sharp (programming language). (2010, November 16). In Wikipedia, The Free Encyclopedia. Retrieved 12:23, November 19, 2010, from http://en.wikipedia.org/w/index.php?title=F_Sharp_(programming_language)&oldid=397032758

For more information, see Microsoft F# developer centre.