I've done most of my development work in F# over the past few years. Most of that was on Windows, but I've done some cross-platform work using F# on Mono (on Fr

I've done most of my development work in F# over the past few years. Most of that was on Windows, but I've done some cross-platform work using F# on Mono (on FreeBSD and Linux). Overall, Mono isn't as fast as the .NET CLR on Windows, but it has improved greatly over the past few years (since Xamarin took over development from Novell and hired a team of full-time developers); in fact, a couple of months ago I saw a post here on HN about an HFT firm who'd built their trading stack on Mono. As for F#, it's usually quite speedy, whether you run it on Windows or Mono (OS X, Linux, FreeBSD, etc.)