The Linux computer operating system. It's all about choice.
Linux is a computer operating system just as Windows for PCs and OSX for Mac. Linux, or GNU/Linux as some prefer to call it works well on PCs and Macs. In fact Linux has been ported to many computer types ranging from cell phones to super computers. This is made possible by the free and open source nature of Linux. Anyone is free to download the source code and alter it as needed to fit a particular need. Thousands of programs are made available by programmers around the world who are willing to donate their time and expertise for the Linux community. These attributes make Linux both free as in “freedom” as well free as in “free beer” as the community likes to phrase it.
Linux can coexist with other systems.
Linux can be installed on the same computer as Windows in such a way that allows the user to decide at boot-up whether to boot Linux or Windows. Both systems can even share data such as music and other files.
Free as in freedom and free beer.
What does it cost the end user? Nothing. It's free as in “free beer”. Many people like to give back to the community in any way they can. This can be advise on information forums, help in writing documentation and how-tos, testing of new releases or free will monetary contributions. Just learning and sharing with others is a contribution in itself.
Can do most anything other OS can do.
What can you do with a computer with Linux installed on it? Most anything. There is software available for Linux that will replace most stuff on other systems. Office tools, music and video editors, graphic and photo editors, Internet and e-mail tools, financial and investment software, games, programming tools. This website was created with Linux software. Well, OK, that's nothing to brag about. I find that I don't need to use any other OS anymore.
Where to get it.
Is it difficult?
Many people think of Linux as being a difficult system to use but many others have found it as easy as any other. Different in some ways as Windows is different from OSX. Some older folks using Linux for the first time do just fine. I migrated from Windows XP at about age 60.
It's all about choice. From the huge selection of software to the many different windowing and desktop environments that allow use with old and slow computers or very new and fast ones. My old Pentium 4 system works just fine as does my really old P3 with light weight desktop environment.