NetBSD is a computer operating system (as are Windows and Mac OS). It's a free version of Unix (as is Linux). The standard Windows-compatible PC is one of the 50 types of computers that NetBSD runs on. About 150 computer nerds around the world — a few lucky ones in the course of their day jobs, but most in their spare time — are allowed to make changes to NetBSD. Soon, I'll be one of them.
It's not a paid position, but there are lots of good reasons for me to accept it. The most practical one is that I use NetBSD, and when it doesn't quite do what I want, now I'll be able to fix it myself. Another reason is that someday I'd like to work at Apple on Mac OS X, which uses a lot of NetBSD's code; being a NetBSD developer will help me become familiar with that code, and will look awfully intriguing on my resume.
But the most compelling reason is that some of the most amazingly brilliant computer programmers I've ever seen are NetBSD developers. There are guys who can look at a new kind of computer, determine what chips are in it and how they're connected, and have NetBSD running on it within a few weeks. I doubt I'll ever be that cool, but damned if I don't want to absorb just a few of the smartatrons flying out of their brains. Being a NetBSD developer, even if my contributions are more prosaic, puts me at close range.