Open Source
MIT/X11
Merlin
[21-Feb-2013,
Beta]

Merlin is a tool
which providessmart completion, among other things, in your favorite editor.
As of today, Vim and Emacs are supported.
GPL
ocamlglobaltags
[15-Jun-2009, version
1.0,
Stable]
A source code tagger for OCaml that can be plugged in to GNU Global's tag set up.
taggage
[26-Aug-2003, version
1.1,
Beta]
Vim tag file generation for OCaml.
Taglet
[27-Aug-2003, version
1.3,
Stable]
OCaml tag file generator.
tuareg imenu
[09-May-2002,
Stable]
Tuareg imenu is an extesion for Emacs of the tuareg mode (it do not work under XEmacs). It help to have an global visoin of you code
Vim support for .annot files
[06-Oct-2003,
Stable]
A ViM extension that is able to parse .annot files and
print the type of an highlighted (visual mode) part of an ocaml source
file.
BSD
LablScintilla
[01-Feb-2007, version
0.9pre1,
Beta]
Caml for Scintilla is a free source and binary package which adds syntax coloring for the Objective Caml language to the multi-platform (Win32 and GTK+) Scintilla editing component and SciTE text editor.
Others
annot
[17-May-2006,
Alpha]
Given a cursor position (line 30, column 20) "annot -type 30 20 main.annot" looks up the type
annotation for that position in main.annot. It is trivial to hook this
to a key in Vim, and probably most other editors.
caml-info-look
[19-Mar-2002, version
0.9]
An Emacs minor mode for automatic look up OCaml Info files.
Camlanot.vim
[24-Sep-2007, version
0.9,
Beta]

A vim plugin to handle annot files.
OCaml mode for NEdit
[28-May-2002]
Smart-indent macros and syntax hilighting for OCaml code with NEdit.
ocaml.vim
[09-Aug-2001,
Stable]
OCaml syntax file for the VIM-editor.
OMLet
[14-Mar-2005, version
0.10,
Beta]
OMLet provides a much better indentation for Caml/OCaml files than the official one. It mostly behaves as tuareg-mode for emacs does. Omlet supports most of the language features, including objects.
Otags
[17-Dec-2012, version
4.00.1,
Stable]
An Emacs tag generator for Ocaml source files, working also with syntaxes extended with Camlp4.
Practical hints for using OCaml
[08-Oct-2001]
Hints which might help you get started with OCaml-development (mostly in UNIX environment).
Tuareg
[01-Jun-2010, version
2.0.1,
Mature]
Tuareg is a Caml mode for GNU Emacs and XEmacs. It handles automatic indentation of Objective Caml and Camllight codes. Key parts of the code are hilighted using Font-Lock. Support to run an interactive Caml toplevel and debbuger is provided.