There is nothing in the definition of free software that indicates that it is free of charge.    
to answer that, most free software we know is free, it is only a repercussion. 
it's the way people have decided to deliver them. 
There are four fundamental freedoms of a free software
The first, freedom is to run it. So once received, we can do with it as we please, there are no limitations, neither for a specific purpose nor in specific circumstances or a specific country, so it can be run it anywhere.    
second freedom is the right to study the software how it works, we must obtain the software's definition, how it works, and so its sources, the original program that allows the building and creating of software that runs. 
software has 2 formats, one is the source format and an executable format,  
The source format allows us to modify how the program behaves and to create it 
the second format is the executable format the one with which we work as a user.
the third freedom is to redistribute If you were given software or if you were sold free software and you use it,  
then you have the source code, and the permission to distribute it to whoever you want in any way you want.
There are no limitations for distributing the software. you even have the right to sell it 
 the fourth and the last freedom is the ability to modify it, upgrade it and transform it. 
So there's no limitation  
we are totally free, so once you've upgraded it, you can distribute it again.   
I'll talk about commonly used software, Firefox, the web browser, is a free solution  
that also has the advantage to run on all platforms, so whatever computer you may have, 
you will be able to find a Firefox suited to your needs  
you only have to learn about one software, and whatever hardware you may buy later, 
you are guaranteed that you will be able to use that software.   
There are other software, to watch videos, for example, VLC, which is a mainstream software for watching videos also broadcast them, and even record them,
so inside VLC, there's a lot of work done on video.  
Libre Office is also a classic, it's an office software application that allows performing the main office uses that we know, so word processing, spreadsheets, presentations.  
The software was originally more or less free, that's the very essence of software to be able to be distributed, exchanged, etc.   
At one point in time, hardware parted hardware providers parted from software providers  
the need to protect, sell full-fledged software
and at that moment, people started to use commercial licenses stating that software could not be used under every circumstance
restricting access to the source code, that modifying software was not authorized, 
only the companies providing the software had the right  work on it, 
all those things came with the advent of great commercial software providers.
Before that, it was much more hardware related, so the creator of free software, of the free software's definition, that's Richard Stallman,  
an American researcher that belonged with an artificial intelligence MIT laboratory, 
he used software and he decided to free as much software as he could  
He defined the 4 freedoms and then funded a foundation, the Free Software Foundation, 
to defend those freedoms 
then he also defined the associated licenses to guarantee those freedoms would be maintained for software and that it could no longer be lost. 
 So yes, Stallman is the pillar of free software, the one who defined what they were.   
Around him, we will find people who worked on GNU 
GNU is a free Unix, at the time when Unix was released, let's say between 71 and 80, a lot of proprietary Unix was released   
so to get access to Unix for everybody, people had to develop free software for Unix,
so that's where it started.  
so now we are on Linux, and Linux is the work that Linus Torvalds a Finnish student, made to complete the GNU offer that did not provide the core, the part that enables to have Unix running on any hardware  
so he completed the GNU offer and so Linux took, along the years, almost every space  
where there were proprietary Unix software and systems.