[mhd]

It is a compiled language with some decent enough unix integration, so this isn't the first system-level program I've seen written in it. The rather popular unison file synchronizer is Ocaml, too, if I'm not mistaken. For a while the most popular Linux client for the edonkey peer-to-peer file sharing network was mldonkey. And just recently I stumbled across a minimal PDF viewer called llpp that turned out to be Ocaml, too.

You can easily distribute packages without huge dependencies, it's not any worse at concurrency than your usual Unix go-to language C, and the FFI ain't half bad, either. It's also relatively unopinionated about IO, which certainly helps writing servers and system utilities.

There's also parsers and some web stuff, but I'll let others talk about this. Just wanted to say a bit about this somewhat surprising niche where the language managed to eke out a bit of a marketing share.