OpenBSD is an operating system that prioritizes security, encryption, and free (as in free and open) software. It's built in the open - anyone can see the code and discussions around it. That's no accident - the earliest contributors recognized that transparency and public discussion are essential to effective security. If you follow the project and the email lists for any length of time, it becomes clear that the core contributors are passionate about security and quality. These are volunteers that spend their limited, precious spare time on building a great operating system that they give away for free because they want to see secure, high quality software thrive in the world. They've been doing it for 20 years.
What they've made works really well. While it's not as easy for a consumer to use as Windows or OS X, to someone more technically inclined, it's straightforward to use as a server or as a desktop for many use cases. And the big feature: it starts our very secure and if you're careful you can keep it that way as you customize it to suit your purpose.
A heartfelt case for OpenBSD.