This is an unofficial working copy of Claude Marché's regular expression library [1]. It is a lightweight and pure OCaml implementation that is reentrant, portable (no C bindings) and fairly fast compared to Str or Pcre [2]. It is not as featureful, however.
[1] http://www.lri.fr/~marche/regexp/ [2] http://www.openmirage.org/wiki/ocaml-regexp