FreeBSD is a free and open-source Unix-like operating system whose objectives are features, speed, and stability. It has a variety of uses on different platforms, and a large community which maintains it.
FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices. — from FreeBSD home page.
Next Open Source Tuesday will feature the Thunderbird project.