Some software meet a standard of excellence and are truly exemplar. That is the spirit of Free Software, the fact that programs can always be revised and improved. I'll make a list of these amazing software that are the state of the art technology of today and a proof of the power of Open Source and Free Software. For this article I will only include software that is notable and non-technical enough for everybody to enjoy.
The short answer is: Linux is the kernel of a free operating system that suits as a replacement for Windows or Mac OS. Both Windows and Mac OS are proprietary software, they are available for sale and the user cannot modify how these operating systems work. The Linux kernel and the GNU applications that run on this alternative operating system are (usually) free of charge and free to be modified by the user or any community of developers. It is built by the users, for the users.