Secure operating system
This article is for operating systems which have achieved a certification from a credible security auditing organization, such as a B2 or A1 CSC-STD-001-83 "Department of Defense Trusted Computer System Evaluation Criteria" or Common Criteria certification.
For Security focused operating systems which do not necessarily have a certification, but which are aimed at security, see the appropriate article.
Trusted Solaris
Trusted Solaris is a security-focused version of the Solaris Unix operating system. Aimed primarily at the government computing sector, Trusted Solaris adds detailed auditing of all tasks, pluggable authentication, mandatory access control, additional physical authentication devices, and fine-grained access control. Versions of Trusted Solaris through version 8 are Common Criteria certified.