In software engineering, a project fork happens when developers take a copy of source code from one software package and start independent development on it, creating a distinct and separate piece of software. The term often implies not merely a development branch, but also a split in the developer community, a form of schism.
Free and open-source software is that which, by definition, may be forked from the original development team without prior permission, without violating copyright law. However, licensed forks of proprietary software (e.g. Unix) also happen.
The word fork stems from the Latin word furca, meaning a "fork or similarly shaped instrument."
"Fork" in the meaning of "to divide in branches, go separate ways" has been used as early as the 14th century.
In the software environment, the word evokes the fork system call, which causes a running process to split itself into two almost identical copies that typically diverge to perform different tasks.
In the context of software development, "fork" was used in the sense of creating a revision control "branch" by Eric Allman as early as 1980, in the context of SCCS: Creating a branch "forks off" a version of the program.
In proprietary software, the copyright is usually held by the employing entity, not by the individual software developers. Proprietary code is thus more commonly forked when the owner needs to develop two or more versions, such as a windowed version and a command line version, or versions for differing operating systems, such as a word processor for IBM PC compatible machines and Macintosh computers.
Generally, such internal forks will concentrate on having the same look, feel, data format, and behaviour between platforms so that a user familiar with one can also be productive or share documents generated on the other.
This is almost always an economic decision to generate a greater market share and thus pay back the associated extra development costs created by the fork.
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