Fork
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 piece of software.
For instance, the above text was forked from the English Wikipedia! Free content licenses allow people to copy material in part or whole to create their own versions of that content: be it a cultural work, a piece of media, software, or some intellectual pursuit.
Sometimes, forking results in fragmentation, whereby two separate communities have overlapping goals. There are strengths and weaknesses to this. On the one hand, different communities can meet different needs and problem-solve in new ways. This also keeps one cultural work from being dominated or controlled by a single individual or small subset of people. On the other hand, fragmentation can create redundancy and confusion amongst people.
Forking starts as mirroring, which is a similar concept where one site hosts identical content to another site.
See also federated wiki.