Free software can otherwise be called open source software. The term “free” when applied to software means that the final user of the programme has the right to do the following without any limit:

1.    Study the source text of the programme,
2.    Change this text,
3.    Copy the original or the changed version of the programme,
4.    Personally distribute the original or changed versions.

               The enumerated freedoms are an integral part of open source software term. It is worth mentioning that none of them provide the right of the author or the final user to sell or gain profit from using it in any other way (for example, by means of paid technical support).
Thus the rules of free software creation and distribution impose certain requirements on that software whereas charge-free software does not have such strict limitations. 
From the point of view of the freedom available for the software final user there is only one right – to receive a copy of the programme free of charge. Other than that the author can impose any limitations on the charge-free software. For example, (s)he can refuse from distributing the original text of the programme thus prohibiting the user from studying the software working principles. Such limitation in its turn makes impossible making changes to the programme code by its final user. Otherwise the author can prohibit copying or distributing his programme. 
Thus despite the fact that open source software can be distributed charge-free, and charge-free software can be open source, these are two different terms, having little in common.