1. ^NeXTSTEP Programming, Step One: Object-Oriented Applications", by Simson Garfinkel and Michael Mahoney
2. ^Getting started PB -> PBX, By Paul R. Summermatter, Mar 25 2001, Cocoabuilder {{404|date=April 2017}} [https://web.archive.org/web/20150429125029/http://www.cocoabuilder.com/archive/cocoa/26936-getting-started-pb-pbx.html Archived]
3. ^[https://books.google.com.au/books?id=onyzCAAAQBAJ&lpg=PA36&ots=p2sINRbQk8&dq=Project%20Builder%20%20IDE%20NeXTSTEP&pg=PA36#v=onepage&q=Project%20Builder%20%20IDE%20NeXTSTEP&f=false Professional Swift] By Michael Dippery, Page 36, Xcode is based on Project Builder, an IDE you use to write programs for the NeXTSTEP operating system, the forerunner of Mac OS X
4. ^[https://books.google.com.au/books?id=ddJxAKUlN-wC&lpg=PA5&ots=kD4uvjlfOw&dq=A%20free%20copy%20of%20Project%20Builder%20was%20bundled%20with%20every%20copy%20of%20OS%20X.&pg=PA5#v=onepage&q=A%20free%20copy%20of%20Project%20Builder%20was%20bundled%20with%20every%20copy%20of%20OS%20X.&f=false Page 5, A free copy of Project Builder was bundled with every copy of OS X.], Xcode 4, by Richard Wentk
5. ^OS X's ten most innovative features, By Macworld Staff, Editors, Sep 13, 2010, Macworld, ...Included in the package was an IDE—Project Builder—that was a tweaked version of the IDE that came with NeXT, the OS whose acquisition laid much of the foundation for OS X. In 2003, Project Builder became the now familiar Xcode...