— I have a plan to use OpenSolaris in this year, but now, the development has been discontinued.
First, OpenSolaris is not, nor related to, Linux. Solaris was primarily based on System V, which incorporated pieces of BSD code as well. Some concepts from SunOS, which was a fork of BSD 4.1, also were implemented in Solaris.
OpenSolaris has been discontinued, but Solaris is available for certain non-commercial, unsupported purposes for free. You can download it from Oracle here.
Since Oracle closed the source code tree during the development cycle, Illumos is the largest fork of the OpenSolaris codebase. OpenIndiana's current release is based on the latest dev code release of OpenSolaris. They (OpenIndiana) have a development release that is based on Illumos.
I don't know if Schillix is built off of Illumos yet, but it is also an option. And there's also Nexenta, if you're looking for something with commercial support, and a strong focus on storage management.
If you are looking for something that is most similar to OpenSolaris, however, Openindiana is it.