Free software is a term coined by Richard Stallman and the Free Software Foundation to refer to software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form. Free software needs to include its human readable source code to fulfill the freedoms. The free software movement was launched in 1983 to make these freedoms available to every computer user.
The software author or distributor can either place no restrictions or use minimal restrictions deemed necessary to ensure that further recipients also get these freedoms. A notable requirement for distributors of free software is to make available the source code to anyone to whom they distribute the software in a non-human readable form. This is called copyleft. The normal way for software to be published as free software is for its source code to be made available with a software licence which grants recipients these permissions: a free software licence.
Everyone is free to sell copies of free software, to use it commercially, and to charge for distribution and modifications. Because anyone who has a copy may distribute the software at no cost, the software generally is available at no cost. Free software business models are usually based on adding value such as support, training, customisation, integration, or certification. However, free software does not allow for common business models that depend on a user having no choice but to pay for a license in order to lawfully use a software product.
The antonym of free software is proprietary software. Free software is not to be confused with "Freeware", which is software made available free of charge. Freeware may or may not be proprietary. From the late 90s onward, some alternative terms for free software came into common usage including "open-source software", "software libre", "FLOSS", and "FOSS".
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