"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 supports binary emulation of most programs from SVR4 (Solaris), FreeBSD, Linux, BSD/OS, SunOS and HP-UX."
"OpenBSD is developed by volunteers. The project funds development and releases by selling CDs and T-shirts, as well as 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."
Once installed, you don't need to configure it to make it secure. It's secure by default and just works out-of-the-box. It's free. It means that you don't have to pay top-dollars to use it. Moreover you are able to support development by donating money, hardware and sending patches.
OpenBSD has everything you need to be secure:
...and many other useful things i just can't count. There are third-party applications available in ports tree.
You can get last news about OpenBSD from its journal.
There are some other BSD projects: