OpenBSD is a free, multi-platform 4.4BSD-based UNIX-like operating system with a focus on security, portability, standardization, code correctness, proactive security and integrated cryptography.
OpenBSD is an open-source operating system derived from 4.4BSD UNIX and is popular for it's focus on security, portability and code correctness. It was forked from netbsd in the mid-1990s.
The project strictly incorporates only source code with ISC or BSD compatible licensing (except the ports tree) with the goal of providing software for any use, including commercial. It is funded by the Canadian non-profit, The OpenBSD Foundation, which also supports related projects such as OpenSSH, LibreSSL, OpenSMTPD, and other popular infrastructure software.
OpenBSD Foundation: http://www.openbsdfoundation.org