No! It’s not a mistake; it’s really F#, the last born from Microsoft Research. F# is a new functional programming language that runs on Microsoft’s Common Language Runtime and the .NET Framework. This means that F# has access to .NET Framework APIs and, conversely, that other .NET languages can use F# libraries.
So, if you are interested in F# or you are just curious, go to this page where you will find all necessary information (fast guide introduction, links to official documentation, Q&A, …)
Have fun with F#.