Project Builder was an integrated development environment (IDE) originally developed by NeXT for the NeXTSTEP operating system. It was rewritten and informally dubbed PBX[1] while distributed by Apple Computer for software development on Mac OS X computer systems prior to Mac OS X v10.3. It was superseded by Xcode, as of Mac OS X 10.3 Panther.
GNUstep's ProjectCenter IDE is a rough workalike of the original NextStep design; additional functionality is provided by ProjectManager, a 3rd-party GNUstep IDE meant for greater usability.
References
Project Builder Wikipedia(Text) CC BY-SA