Data file created by Xcode, a development application for Mac OS X; saves project data such as the list of source code and resource files and the build properties; also saves the Group data, which organizes the resource files in a virtual folder hierarchy. Even though the Xcode interface shows the project.pbxproj file for the project in the IDE's user interface, the actual PBXPROJ file is stored within the .XCODEPROJ file for the project.