Contrary to popular opinion that nothing worthwhile is ever written in non-imperative languages, CAML, or rather, the OCAML implementation of it, it used to in the p2p file-sharing program MLDonkey, a free client for the eDonkey network.
Of course, to those opposed to the legally-precarious topic of file-sharing, it still true that nothing worthwhile has ever been written in a non-imperative language. However, it still remains that the eDonkey2000 network is probably the file-sharing network.
But I digress.
This has always been one of the flaws of MLDonkey, since anyone who wanted to compile the program from CVS would have to have a OCAML compiler and the OCAML version of the gtk library. From personal experience it is slightly less fun than installing Gentoo — the latter has the thrill of installing an entire system.
I'm reliably informed (by the website as cited in the top wu) that OCAML is the best thing since sliced bread; I have yet to meet one single programmer who works extensively with the language.