At first glance, this looks like Dropbox or OneDrive, but Resilio Sync (formerly BitTorrent Sync) skips one aspect—it syncs file between computers without the files ever hitting a server on the Internet for online storage. This is purely peer-to-peer syncing, and works great with large files. For free, you get syncing between two devices but with unlimited data.

Facebook Messenger is built right into the interface on Facebook on the Web, so you can use it without doing anything special. But downloading the mobile clients or using the dedicated Web interface at opens up lots of other options, from voice and video calls, to SMS texting support, to use of stickers, to, perhaps the best part, chatbots that will talk to you and provide info. Like its brother, WhatsApp, it also has a billion users.
Rules about how to package a modified version are acceptable, if they don't substantively limit your freedom to release modified versions, or your freedom to make and use modified versions privately. Thus, it is acceptable for the license to require that you change the name of the modified version, remove a logo, or identify your modifications as yours. As long as these requirements are not so burdensome that they effectively hamper you from releasing your changes, they are acceptable; you're already making other changes to the program, so you won't have trouble making a few more.
Practically the de facto reader for ebooks these days, the Kindle brand is more than just hardware—it extends to these apps and programs for reading ebooks (which you have to buy from Amazon, of course). Start the book on any device, continue it elsewhere—the Kindle WhisperSync feature knows where you stopped reading. X-Ray gives you insight into the book; GoodReads integration gives you a social aspect. The new PageFlip lets you keep your page while scouring the rest of the book.
Up to three people on their PCs can use the browser to video chat and even share screens, all without fees or any setup other than sharing a URL. Sign up for an account or sign in with your Google or Facebook accounts, and you can claim a regular-to-use meeting "room" online. Because it's Web based, it works for Linux, Mac, or Windows, even on a Chromebook.
PCMag's top pick for software to take control of other computers is TeamViewer. Almost everything you need is free: desktop sharing, file transfers, even chat with remote users. And the setup couldn't be easier. Take control of a PC over a Web connection and a Chrome browser (even in ChromeOS) with the TeamViewer extension. There is also a Windows app in the Microsoft Store and optional downloads to make installing TeamViewer on multiple PCs even easier—though it's only free for personal use.
The Debian project is a strong supporter of free software. Since many different licenses are used on software, a set of guidelines, the Debian Free Software Guidelines (DFSG) were developed to come up with a reasonable definition of what constitutes free software. Only software that complies with the DFSG is allowed in the main distribution of Debian.
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.