The most recent version of OCaml is 4.00.1.
It was released on 2012-10-05.
What's new?
Some of the highlights in release 4.00 are:
- The name of our favorite language is now offically "OCaml", and
this name
is used consistently in all the documentation and tool outputs.
- Generalized Algebraic Data Types (GADTs): this is a powerful
extension of the type system that provides great flexibility and power
to the programmer.
- A new and improved ARM back-end.
- Changes to first-class modules: type annotations can now be omitted
when packing and unpacking modules (and are inferred from context
whenever possible), and first-class modules can now be unpacked by
pattern-matching.
- Support for randomized hashtables to avoid denial-of-service
vulnerabilities.
- Installation of the compiler's internal libraries in
+compiler-libs for easier access by third-party
programming tools.
For more information, please consult the comprehensive list of changes.
Distribution

Source distribution
-
Source tarball (.tar.gz)
for compilation under Unix (including Linux and MacOS X)
and Microsoft Windows (including Cygwin).
-
Also available in .tar.bz2
format.
- GODI
is a source-based distribution of OCaml and
many companion libraries and tools. Compilation and
installation are automated by a powerful package manager.
The INSTALL file of the distribution
provides detailed compilation and installation instruction.

Precompiled binaries for Linux

Precompiled binaries for MacOS X
Binary package
compiled on Mac OS 10.7.5 with XCode tools
4.4 (probably not compatible with earlier versions
of Mac OS X):

Precompiled binaries for Microsoft Windows
Four ports of OCaml for Microsoft
Windows are currently available. For additional information,
please consult the list of portability issues or
the Windows release notes.
-
Cygwin-based native Win32 port
(4.00.0).
A self installer. The interactive loop comes with a
simple graphical user interface. Some features require the Cygwin
environment, which the installer can fetch for you. However, the
compilers are, and generate true Win32 executables, which do not
require Cygwin to run.
-
Microsoft-based native Win32 port.
No binary distribution available yet;
download the source distribution and compile it.
-
Cygwin-based port.
Requires Cygwin.
No graphical user interface is provided. The compilers
generate executables that do require Cygwin.
The precompiled binaries are part of the Cygwin distribution;
you can install them using the Cygwin
setup
tool. Alternatively, download the source distribution
and compile it under Cygwin.
-
Microsoft-based native Win64 port
Same features as the Microsoft-based native Win32 port,
but generates 64-bit code. No binary distribution available
yet; download the source distribution and compile it.

User's manual
The user's manual for OCaml can be:
Other versions
Many previous releases are still available.
You also have read-only SVN access
to the working sources and to all previous public releases. See:
The Subversion repository for OCaml