Mailing Lists and Forums
Mailing lists and other forums used to discuss OCaml in general are listed below. There are thousands of other forums related to individual projects. Several mailing lists are hosted on the lists.ocaml.org domain. Projects on GitHub actively use GitHub's Issue system for discussions.
Official OCaml List
caml-list AT inria.fr
The OCaml mailing list is intended for all users of the OCaml implementations developed at Inria. The purpose of this list is to share experience, exchange ideas and code, and report on applications of the OCaml language. This list is not moderated, but posting is restricted to the subscribers of the list. Messages are generally in English but sometimes also in French. In 2010, the list has about 1500 subscribers, who exchange about 300 messages per month.
The OCaml Weekly News also provides a curated summary of caml-list discussions.
ocaml_beginners AT yahoogroups.com
This list is a place for the mutual aid of those who recognize that they're not OCaml gurus yet... everything you wanted to ask about OCaml, but were afraid to submit in the more official caml-list AT inria.fr, can be asked, answered and discussed here. In early 2004, the list has about 300 subscribers, who exchange about 100 messages per month.
OCaml Jobs and Internships
ocaml-jobs AT inria.fr
This list is for exchanges between people looking for a job or an internship requiring skills in OCaml and people, corporations, universities, ..., offering such jobs or internships.
caml-announce AT inria.fr
This is a low-traffic, moderated list for announcements of OCaml releases and new OCaml-related software, libraries, documents, etc.
IRC Channel - English
This is a real-time communication channel, where you can ask for help. There are about a hundred users hanging around; don't ask if you can ask, just ask, and be patient: not everyone is in the same timezone. The IRC Channel can be accessed through a web interface or any regular IRC client.
Public channel logs are available at http://irclog.whitequark.org/ocaml/
If you wish to use a web-based IRC client, you can use Freenode's webchat https://webchat.freenode.net/. For a fancier/nicer interface, you may try https://vector.im/beta/#/room/#freenode_#ocaml:matrix.org -- it requires registration but is otherwise free.
IRC Channel - French
As above, but for French speakers.
This is a moderated Usenet newsgroup about all variants of ML. Discussions generally concern Standard ML implementations (such as SML-NJ), but some threads concern the OCaml branch.
About Functional Languages
This is an unmoderated usenet newsgroup for the discussion of all aspects of functional programming languages, including their design, application, theoretical foundation, and implementation. Discussions concern all families of functional programming languages including non-strict ones (e.g. Haskell) and strict ones (e.g. Scheme, SML or OCaml).
Mantis Bug Tracker
Inria manages the official distribution of OCaml and uses Mantis to track bugs and feature requests.