illumos is a fully open community project to develop a reliable and scalable operating system. It began as a [http://en.wikipedia.org/wiki/Fork_%28software_development%29 fork] of the former [http://www.opensolaris.org/ OpenSolaris] operating fork of the former OpenSolaris operating system.
Our goal is to foster open development of technologies for the 21st century while building on a twenty-year heritage, but free from the oversight of a single corporate entity and the resulting challenges thereof.
The illumos code base forms the foundation of distributions including a storage appliance from [http://www.nexenta.com/ Nexenta] Nexenta, a cloud platform from [http://joyent.com/ Joyent] Joyent, and the general-purpose [http://openindiana.org/ OpenIndiana]. OpenIndiana.
To use the operating system, just download and install one of the distributions. [http://openindiana.org/ OpenIndiana] is OpenIndiana is a general-purpose system suitable for users and developers. Joyent has [http://smartos.org/ SmartOS ] for SmartOS for hosting applications and virtual machines, and the [https://github.com/joyent/illumos-live illumos-live] build build system that constructs a bare-bones system image.
Is illumos free software (open source)?
The bulk of the illumos source code is available under the [http://en.wikipedia.org/wiki/Common _ Development _ and _ Distribution _ License Common Development and Distribution License (CDDL)], an OSI-approved [http://en.wikipedia.org/wiki/Free_software free software ] free software license based on the Mozilla Public License (MPL).
illumos thrives on the efforts of its contributors. Have a look at the guide on [[How to To Contribute]] if if you want to submit code. If you want to help in other ways then have a look at the [[Mailing Lists]] and [[irc channels]] to and other ways to contact us to see if there is are any other places where help is needed.
Most of the developers can be found on irc, IRC and you're invited to drop in and say "hi!".
How do I build illumos?
See How To Build illumos.