There are many schools of thought in the free software movement, and
there is a certain amount of bigotry amongst adherents of the various
religions. I think there's room for all flavours, although I normally
use either the GNU or BSD licences.
Because the GNU GPL was an early and influential licence, I have
provided some information about it here; below, there are pointers to
some other information.
“Free software” is a matter of liberty, not price.
To understand the concept, you should think of “free
speech”, not “free beer.”
“Free software” refers to the users’ freedom to run, copy,
distribute, study, change and improve the software. More precisely,
it refers to four kinds of freedom, for the users of the software:
- The freedom to run the program, for any purpose (freedom
- The freedom to study how the program works, and adapt it to your
needs (freedom 1). Access to the source code is a precondition
- The freedom to redistribute copies so you can help your neighbor
- The freedom to improve the program, and release your improvements
to the public, so that the whole community benefits. (freedom 3).
Access to the source code is a precondition for this.
A program is free software if users have all of these freedoms.
Thus, you should be free to redistribute copies, either with or without
modifications, either gratis or charging a fee for distribution, to
anyone anywhere. Being free to do these things means (among other
things) that you do not have to ask or pay for permission.
You should also have the freedom to make modifications and use them
privately in your own work or play, without even mentioning that they
exist. If you do publish your changes, you should not be required to
notify anyone in particular, or in any particular way.
The freedom to use a program means the freedom for any kind of person
or organization to use it on any kind of computer system, for any kind
of overall job, and without being required to communicate subsequently
with the developer or any other specific entity.
The freedom to redistribute copies must include binary or executable
forms of the program, as well as source code. (It is ok if there is no
way to produce a binary or executable form, but people must have the
freedom to redistribute such forms should they find a way to make them.)
In order for the freedoms to make changes, and to publish improved
versions, to be meaningful, you must have access to the source code of
the program. Therefore, accessibility of source code is a necessary
condition for free software.
In order for these freedoms to be real, they must be irrevocable as
long as you do nothing wrong; if the developer of the software has the
power to revoke the license, without your doing anything to give
cause, the software is not free.