I have compiled 23 of the most outstanding free/open source software. If these software have price tags, I would consider them the most expensive and valuable. The list was judged according to how I view their significance in the field of technology and the benefits that they have given to society. Some disclaimer: The most valuable free software list is based on my opinion alone and no survey was done. However, I did some extensive research to support my judgment.
Free software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions only to ensure that further recipients can also do these things. To make these acts possible, the human readable form of the program (called the source code) must be made available and the software must be accompanied by a software licence saying that the copyright holder permits these acts (a free software licence). Software can also be free software by putting the source code in the public domain.
Alternative terms for free software have been coined in an attempt to make the use of "free" less ambiguous. The most common is "open-source software", which has since evolved to refer to a subtly different sense of freedom. Free software is also known as "software libre", "free, libre and open-source software" ("FLOSS"), and "free/open-source software" ("FOSS").
The 23 Most Valuable Free Software ( in no particular order):
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