The first of a few Piriform programs on this list, CCleaner—the first C is for Crap!—is one of the best, and pretty much essential for keeping a system going. What it does is simple: it cleans up extraneous files to keep a system running better. Get it and run it, regularly. It'll even delete some apps you didn't think you could get rid of—like those provided in Windows 10, whether you wanted them or not.
Copyleft licenses, with the GNU General Public License being the most prominent: the author retains copyright and permits redistribution under the restriction that all such redistribution is licensed under the same license. Additions and modifications by others must also be licensed under the same "copyleft" license whenever they are distributed with part of the original licensed product. This is also known as a viral, protective, or reciprocal license. Due to the restriction on distribution not everyone considers this type of license to be free.
The Free Software Foundation encourages selling free software. As the Foundation has written, "distributing free software is an opportunity to raise funds for development. Don't waste it!". For example, the FSF's own recommended license (the GNU GPL) states that "[you] may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for a fee."
Note: In February 1998 a group moved to replace the term "Free Software" with "Open Source Software". This terminology debate reflects underlying philosophical differences, but the practical requirements placed on software licenses, and the discussion in the rest of this page, are essentially the same for both Free Software and Open Source Software.
Freeflys: Another strong contender in the freebies space, Freeflys has appeared on NBC’s Today Show, The Doctors, Fox News and a handful of other media outlets. Similar to most of these sites, Freeflys utilizes email alerts to tell users about free-sample offers as they happen. The site also allows you to search for a specific product with the handy search bar.