A project fork occurs when software developers take a copy of source code from one software package and use it to begin an independent development work that is maintained separately from its origin. Although forking in open source software does not require the permission of the original authors, the new version, nevertheless, competes for the attention of the same developers that have worked on the original version. The motivations developers have for performing forks are many, but in general they have received little attention. In this paper, we present the results of a study of forks performed in SourceForge (http://sourceforge.net/) and list the developers’ motivations for their actions. The main motivation, seen in close to half of the cases of forking, was content modification; either adding content to the original program or focusing the content to the needs of a specific segment of users. In a quarter of the cases the motivation was technical modification; either porting the program to new hardware or software, or improving the original.