Sun Solaris

Oracle Solaris Open Source Projects on java.net
Sunfreeware for Solaris - Introduction
Oracle Solaris 11 - First Cloud Operating System | Oracle - OpenStack distribution.
Oracle Solaris Zones - Oracle Solaris Zones, previously known as Solaris Containers, are an integral part of the Oracle Solaris 10 operating system (OS).

illumos - OpenSolaris

illumos Home - illumos - illumos wiki
OpenIndiana - is a successor to and derived from the original Sun OpenSolaris reference distribution, and is suitable for use on Servers and Desktops.
SmartOS - from Joyent is an open-source illumos distro designed for cloud computing. It includes a port of KVM, allowing other OSes such as Linux and Windows to run natively in SmartOS/illumos virtualized environments.