OpenIndiana is a continuation of the OpenSolaris operating system. It was conceived during the period of uncertainty following the Oracle takeover of Sun Microsystems, after several months passed with no binary updates made available to the public. The formation proved timely, as Oracle discontinued OpenSolaris soon after in favour of Solaris 11 Express, a binary distribution with a more closed development model to debut later this year.
As you can see from the screenshots, it's essentially OpenSolaris with a few icons and images changed. This is expected given it's initial code base is the snv_147 build of OpenSolaris.
Time will tell how OpenIndiana evolves and grows. Who knows, maybe it'll become the Ubuntu of the Solaris world.