OpenBSD

Why would a Linux user contribute to the OpenBSD project? Here are a few reasons:

OpenSSH

Without an open-source implementation of this protocol, we would still be using telnet and rsh. There are now several free-software implementations, but OpenSSH was implemented early and was good enough that it was widely adopted.

Code Audits

The OpenBSD project audits the code used in its core system, which is an important practice. Much of that code does not make it into Linux. But some of it does, and the bugs that the OpenBSD team finds are reported and fixed, which makes subsequent releases more secure.

Alternatives and Innovation

Alternative implementations of ideas makes for a richer ecosystem, and OpenBSD has contributed its fair share of innovation. For example, the pf firewall and its offshoots (like spamd) stand out here and serve as a benchmark for other open-source implementations.

You might have issues with the OpenBSD project, its approach to full disclosure, or the attitude of its developers. But it is hard to argue that the project has not contributed a fair amount to the way we approach security and to FLOSS overall.

The project accepts donations: http://www.openbsd.org/donations.html