F# is not like Ruby/Python at ALL. F# is statically typed for one, variables are by default immutable, let me give you an example, tell me what you think the following prints?

  let somefunc() =
    let i = 10
    i = 11
  printfn "%s" (somefunc().ToString())

it prints "false", not 11.

F# is a lot like ocaml, which it was syntax compatible with for many years.

Most developers in the non-web sphere are dealing with multi-core and async issues. F# solves these problems very elegantly.