FreeBSD is awesome!
I've built a firewall and dhcp router using FreeBSD! The boxes are really stable and have long long uptimes!
In general, FreeBSD is a free OS based on the UNIX developed at UC Berkeley in the early 80s. The OS is good enough that it can let it be both a PC and a server, both at the same time! Meaning it allows for networking and normal end-user tasks at the same time! 🙂
FreeBSD is used by Yahoo!, MCI WorldCom servers, and many others all around the world. Go to netcraft.com and you can see which computers have the longest uptimes... most are BSD based!
But the best thing is FreeBSD is FREE!! (obviously) My favorite thing was that all you need is two floppies and a network connection, and you can install the OS just with that! You don't need to download ISO images for CDs, just have two floppy disks in hand and a network connection and you can use it. I'm sure other OSes have this feature as well, but it is very simple in FreeBSD.
Hope this is sufficient for your question. 😎