Parabola GNU/Linux-libre is the latest OS to be listed by the Free Software Foundation as meeting their guidelines for a fully free software OS.
From the official announcement at FSF:
Parabola strives to keep its packaging and management tools as simple as possible, so that users have plenty of flexibility to install and configure >the system to their liking. It's based on Arch, and provides instructions for current Arch users to migrate to Parabola and remove any nonfree >software they might have installed. A small team of hackers has come together to build and maintain the distribution.
Parabola GNU/Linux incorporates the KISS principle and rolling release distribution model of Arch Linux. With Parabola GNU/Linux you have the total freedom of Libre software with all the control you need by building your system yourself step by step. The packaging and management tools are transparent allowing you to know precisely what is installed on your system.
Thank you to everyone who contributed in working on the distribution, and most of all thanks to all of you who tried it out and supported us!
Here's a link to the Free System Distribution Guidelines.
Here's a link to the other Free Systems approved by FSF.