For a fully free desktop OS, try Trisquel GNU/Linux 6.0
Linux is widely referred to as a free and open source operating system, but most Linux distributions, or flavors, aren't actually entirely free.
Yes, they're certainly free in price (unless, of course, you choose to purchase commercial support or other services), but when it comes to the other sense of “free”—namely, your freedom to share, study, and modify it—most don't quite make it thanks to the presence of occasional proprietary firmware, drivers, and applications.
There are a few exceptions, however, and they're essentially the only ones of which the Free Software Foundation fully approves. One of the better-known examples is called Trisquel, and it just rolled out a major new update.