OpenSolaris (www.opensolaris.org) is the open source initiative endorsed by Sun and its key developers. Its first release was open to the public this June 14.
OpenSolaris's codebase is public available, searchable, and web browsing enabled.
The buz bebind OpenSolaris is the fact that Solaris 11 and OpenSolaris will based on the Project Nevada codebase, which is the next major release of Solaris.