Solaris
Solaris is a Unix variant created by Sun Microsystems. Solaris itself is not inherently security-focused. Majority of Solaris source code has been released via the OpenSolaris project, mostly under the Common Development and Distribution License. Enhancements to OpenSolaris, both security related and others, are backported to the official Solaris when Sun certifies their quality.
Read more about this topic: Security-focused Operating System