OpenBSD

OpenBSD is a free open source operating system based upon the Berkeley Software Distribution (BSD) for UNIX.

The OpenBSD project, coordinated by Theo de Raadt, is known in the programming community for its attention to security. His team is perhaps best known for developing OpenSSH, an open-source secure shell daemon for encrypting network packets.

The project is also known for introducing several important changes to the way the rest of the open source community works, including providing public access to content version control (CVC) repositories and commit (code change) logs. Because OpenBSD is both compact and secure, one of the most common reasons for implementing OpenBSD is as a firewall.

According to OpenBSD.org:

OpenBSD is developed by volunteers. The project funds development and releases by selling CDs and receiving 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.

The OpenBSD logo and mascot is a pufferfish named "Puffy."

MORE INFO:
> OpenBSD may be downloaded from OpenBSD.org.
> The OpenBSD Foundation supports OpenBSD and related projects like OpenSSH, OpenBGPD, OpenNTPD, and OpenCVS.
> Wikipedia's entry for OpenBSD provides more technical information and history of the distribution.
> Get an executive summary of what's new in OpenBSD 4.1 at the Enterprise Linux Log.