From the [Ocaml website]:
Caml is a strongly-typed functional programming language from the ML family. OCaml (Objective Caml) and Caml Light are two open source implementations of Caml developed at INRIA Rocquencourt, projet Cristal.
I find Ocaml fun to program in because the strong typing catches a lot of errors, and it is possible to write programs that read almost like lists of equations, in common with most functional programming languages. In addition, Ocaml is impure so imperative features can be used if necessary (e.g. for IO or working with matrices).