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."
Software that is free only in the sense that you don't need to pay to use it is hardly free at all. You may be forbidden to pass it on, and you are almost certainly prevented from improving it. Software licensed at no cost is usually a weapon in a marketing campaign to promote a related product or to drive a smaller competitor out of business. There is no guarantee that it will stay free.
The best thing about some of these companies is that you don't have to "Like" them on Facebook, send messages on Twitter, or complete surveys. With the companies I've listed first, simply sign in, input your mailing information, and wait for the free sample to show up in your mail). It will take less than 15 minutes sign up and up to six weeks for samples to arrive.
Play the "Webquiz" to request a free sample of Nikwax Down Wash Direct, which is a "high performance cleaner for both regular and hydrophobic down filled items." You can repeat the quiz as many times as you want and you can win a maximum of one free product per household every two months. The Webquiz is open to those aged 18 and over. Offer is open to residents in the U.S., U.K., Canada, Germany, Switzerland, Austria, Denmark, Netherlands, Belgium, Luxembourg and Poland.