The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like OS.
Edit By BS Editor: The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. Our efforts emphasize portability, standardization, correctness, proactive security and integrated Cryptography.
OpenBSD is freely available from our FTP sites, and also available in an inexpensive 3-CD set.
The current release is OpenBSD 4.8 which was released November 1, 2010.
OpenBSD is developed entirely by volunteers. The project pays for the development environment and developer events by selling CDs through a collection of stores and by accepting donations from organizations and individuals. These finances ensure that OpenBSD will continue to exist, and will remain free for everyone to use and reuse as they see fit. T-shirts and posters are available as well, but do not fund the project.