NetBSD

NetBSD is an open-source operating system based on 4.4BSDlite2. NetBSD is most well known for being able to install on any architecture. This means it not only will work on your PC, it will also work on anything from your PDA to a playstation 2. There is a documented list of supported platforms here.

NetBSD Official website

The current NetBSD release is 6.0.1.