OpenIndiana is a robust enterprise operating system, based on the illumos kernel. It is open source, free to use, community developed, and suitable for servers and desktops.

SmartOS is a specialized Type 1 Hypervisor platform based on Illumos. It supports two types of virtualization:

• OS Virtual Machines (Zones): A light-weight virtualization solution offering a complete and secure userland environment on a single global kernel, offering true bare metal performance and all the features Illumos has, namely dynamic introspection via DTrace
• KVM Virtual Machines: A full virtualization solution for running a variety of guest OS's including Linux, Windows, *BSD, Plan9 and more

OpenSXCE OpenSolaris for SPARC.

OmniOS builds on Illumos to make a complete operating system.
OmniOS - Release Notes
OmniOS - Release Schedule

Solaris Internals and Performance FAQ

rootpool - the blog of Joerg Moellenkamp
Robert Milkowski's blog

Oracle - Solaris Blog
Oracle - Solaris Blog - Technologies

Information Channel - How to Format a Disk in Solaris Operating System