Objective Caml

Cameleon
An IDE specially designed for OCaml.
http://pauillac.inria.fr/~guesdon/Tools/cameleon/cameleon.html

Camomile
Full Unicode Standard 3.2 library for OCaml. English, Japanese. [Open Source, LGPL]
http://camomile.sourceforge.net/

COCAN: The OCaml Alliance Network
Business-focused wiki on OCaml: why managers should choose it, lists of people and firms who use it, how to install on various operating systems, technical resources, user groups.
http://wiki.cocan.org/

CocOCaml
A Cocoa based wrapper for the OCaml toplevel environment. It was written to solve a number of the problems one usually runs into while running the toplevel under OS X's terminal.
http://www.cs.unm.edu/~wneumann/cococaml/

Developing Applications with Objective Caml
By Emmanuel Chailloux, Pascal Manoury, Bruno Pagano; O'Reilly, 2005. Book online. Many topics and examples covered. One drawback: based on old OCaml version. HTML, PDF.
http://caml.inria.fr/pub/docs/oreilly-book/

G'Caml
O'Caml compiler variant, extends ML polymorphism from parametric to non-parametric (extensional). More complex parametricity gives many features impossible or very hard to achieve otherwise: overloading, e.g., type safe value marshalling, ML value printer.
http://www.yl.is.s.u-tokyo.ac.jp/~furuse/gcaml/

The JoCaml System
Experimental OCaml extension, distributed join-calculus programming model; high-level communication and synchronizing channels, mobile agents, failure detection, garbage collected. Descriptions, documents, downloads.
http://moscova.inria.fr/jocaml/

LablGTK
OCaml Gtk+ interface.
http://wwwfun.kurims.kyoto-u.ac.jp/soft/olabl/lablgtk.html

Merjis Ltd.
Has mod_caml OCaml bindings for Apache API, lets you run CGI scripts written in OCaml directly in Apache webserver; and OCaml tutorial, practical, detailed, for those who already know an imperative or OO language.
http://www.merjis.com/developers/

MlGtk
An interface between OCaml and the Gtk+ toolkit
http://cristal.inria.fr/~cuoq/mlgtk.html

Objective Label
Extension of OCaml with labeled and optional parameters, and polymorphic variants and methods.
http://wwwfun.kurims.kyoto-u.ac.jp/soft/olabl/

OCaml Advocacy
Lists many advantages, some shortcomings.
http://www.rouquier.org/jb/programmation/ocaml-pub.php

OCaml for Scientists
This book teaches the fundamentals of programming using OCaml, assuming little prior knowledge of computer programming. Particular emphasis is placed upon programming paradigms rarely seen in current scientific computing, such as exceptions, polymorphism, higher-order functions, nested functions, pattern matching and modules.
http://www.ffconsultancy.com/products/ocaml_for_scientists/

OCaml Link Database
Large, indexed, sorted repository of software contributions for OCaml community. Descriptions, downloads, author contacts.
http://funlinks.camlcity.org/

OCaml Software
Includes functional libraries, interfaces to PostgreSQL, LAPACK, Perl regexps; OCamlMakefile, and syntax files for VIM. By Markus Mottl.
http://www.ocaml.info/home/ocaml_sources.html

O'Jacare
Object-oriented interface between OCaml and Java, code generator to aid interoperability via their object models, defines an IDL and allows a safety execution by static typechecking.
http://www.pps.jussieu.fr/~henry/ojacare/index.en.html

omlet.vim
VIM syntax file for OCaml.
http://www.vim.org/scripts/script.php?script_id=1196

Perl4Caml
Allows using any CPAN Perl code within OCaml.
http://merjis.com/developers/perl4caml/

Programming with Objective Caml
Home of GODI advanced programming environment for OCaml; news, projects with downloads, links, source tree.
http://www.ocaml-programming.de/

Pycaml
Lets users build native OCaml libraries and use them from Python and conversely.
http://pycaml.sourceforge.net/

Yahoo Groups: OCaml_beginners
Email forum for mutual aid of those who know they're not OCaml gurus yet.
http://tech.groups.yahoo.com/group/ocaml_beginners/