Open source software versus free software

Open source software and free software are different terms for software which comes with certain rights, or freedoms, for the user. They describe two approaches and philosophies towards free software. Open source and Free software (or software libre) both describe software which is free from onerous licensing restrictions. It may be used, copied, studied, modified and redistributed without restriction. Free software is not the same as freeware, software available at zero price.

The definition of open source software was written to be almost identical to the free software definition. There are very few cases of software that is free software but is not open source software, and vice versa. The difference in the terms is where they place the emphasis.

"Free software" is defined in terms of giving the user freedom. This reflects the goal of the free software movement. "Open source" highlights that the source code is viewable to all and proponents of the term usually emphasize the quality of the software and how this is caused by the development models which are possible and popular among free and open source software projects.

Free software licenses are not written exclusively by the FSF. The FSF and the OSI both list licenses which meet their respective definitions of free software. Open source software and free software share an almost identical set of licenses. One exception is an early version of the Apple Public Source License, which was accepted by the OSI but rejected by the FSF because it did not allow private modified versions; this restriction was removed in later version of the license. There are now new versions that are approved by both the OSI and the FSF.

The Open Source Initiative believes that more people will be convinced by the experience of freedom. The FSF believes that more people will be convinced by the concept of freedom. The FSF believes that knowledge of the concept is an essential requirement, insists on the use of the term free, and separates itself from the Open Source movement.

The Open Source Initiative believes that free has three meanings: free as in beer, free as in freedom, and free as in unsellable. The problem with "Open Source" is it says nothing about the freedom to modify and redistribute, so it is used by people who think that source access without freedom is a sufficient definition. This possibility for misuse is the case for most of the licences that make up Microsoft's "shared source" initiative, and to a lesser extent with the "license-free" software of Daniel J. Bernstein.