Operating System, that is!
You can download it then install it onto a CD or USB drive. Boot from that CD or USB drive and it has a fully working DOD-built Linux operating system, including office and form software. Even has CAC reader and wifi drivers. When you turn the computer on, watch closely, it will tell you either F2 or F12 will be the key to hit to get the boot options.
Basically, you can do work without having to use windows- dont' know if it works on Macs or not. Don't have to worry about viruses, and when you turn off the computer (or reboot) and take your CD or thumbdrive, no one can see what you were working on.
And, you can sign up for email updates to get notified when they release new versions. They only send the emails every 2-3months or so.