NetBSD is a free, secure, and highly portable Unix-like Open Source operating system available for many platforms, from 64-bit Opteron machines and desktop systems to hand held and embedded devices. While I haven't yet gotten around to trying out NetBSD (I have used FreeBSD and OpenBSD), it is not any lesser in importance than its other counterparts.
In more ways than one, NetBSD has lots of similarities with OpenBSD than with FreeBSD. But NetBSD is said to have a more user friendly installer than OpenBSD, it is available for download as ISO images and it supports the largest variety of devices out there. In fact, NetBSD claims to run on 54 different system architectures featuring 17 machine architectures across 17 distinct CPU families, and is being ported to more.... whew !!