OpenSolaris was based on Solaris, which was originally released by Sun in 1991. Solaris is a version of UNIX System V Release 4 (SVR4), jointly developed by Sun and AT&T to merge features from several existing Unix systems. It was licensed by Sun from Novell to replace SunOS.
OpenSolaris is a descendant of the UNIX System V Release 4 (SVR4) code base developed by Sun and AT&T in the late 1980s. It is the only version of the System V variant of UNIX available as open source. OpenSolaris is developed as a combination of several software consolidations that were open sourced subsequent to Solaris 10. It includes a variety of free software, including popular desktop and server software. Sun has announced that future versions of its commercial Solaris operating system will be based on the OpenSolaris project.