FileInfo.com - The File Extensions Resource

.XCODEPROJ File Extension

File Type	Xcode Project
File Format	File
Common?	No
File Description	Software development project for Mac OS X created with Apple's Xcode programming software; extension used by Xcode 2.1 and later
Program(s) that open xcodeproj files	Mac: Apple Xcode 2.1 or later

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/xcodeproj