Free software does not constitute an economic model in itself.  
It's not an economical matter,  but rather an ethical matter.  
Today, free software has developed so much and it is so easy and convenient to use free software that even commercial companies use it a lot.  
We are going to talk about 2 kinds of free software.  
There is a great split in free software regarding copyleft.  
Copyleft is the principle through which free software keeps its free software characteristic.    
Once it is redistributed, the license can be changed, or not.  
because If it is in copyleft, it has to stay free.  
If it is not in copyleft, it can be used for commercial ends.   
And in practice, all BSD licenses are very much used for business.  
So they can be found in many software, even in proprietary systems cells because they have been reused.   
So now, all you have to do is mention it. 
The software's original sources can be provided, but we are not obliged to submit the modifications that were done or even the way that software was integrated inside our proprietary software.  
So that's a first part. 
So that allows some companies to save money and concentrate on the contributions they can make, and not on what already exists. 
that creates general programming platforms where you can just reuse and start working from there.  
Now when free software stays in copyleft, it also holds an interest in an economical model for all companies doing what we call dual licensing.   
Meaning they sell their software under 2 licences. 
A proprietary one that they sell, which they make mark-up with.   
Which they are going to make other things with.  
They often provide associated services, literature, training, that kind of thing.  
And all the improvements they make, they provide, freely, the copyleft.   
That one cannot be used in proprietary mode, but it can be used and distributed freely. That's one of the free software models that work      
François Elie wrote a book on the subject called  Free software economy  
which defines 4 models and he describes 2 of those models as being stable,
and the other  2 models being more unstable. 
What makes unstable models unstable is the fact people freely contribute to the software and upgrade it without remuneration.   And after that, someone builds all that software and sells it. So that's a rather unstable model.  
There are foundations where a lot of companies are interested in having a common pot of tools.    
There are large foundations like Apache, the Mozilla foundation in which you can find 
gigantic companies that invest money so that the foundation endures.
in order to keep the software on the market.  
A large part of the developers are actually employees and contribute.  
That is one-way companies can behave.
 They can either put money in free software, or they can provide a developer who will also work on the software, so it brings to the community, we can even say to humanity, common knowledge and software.    
That's the shared foundation of free software. On top of that, everybody adds his own contribution and what makes it alive.   
There are other solutions. One of the cloud's operating modes is that end-users use the service but do not actually use the software.   
So end-users pay directly or indirectly, either by having their personal data collected and selling it one way or another, by using it for advertising, that's Google's model.  
Services can also be paid directly if the software is free for the people who install it on their servers, but not for the end-user. In the cloud, in all services, there is an abundance of free software  
it's huge and it doesn't stop business, big business to run along with it.  
Those are all the economic models, there are certainly others and more are yet to be invented.The economical model is indeed is a complicated thing.