Project Builder

Apple's (née NeXt's) IDE for MacOsx. A beautiful, simple IDE without many frills, it has features useful for an IDE:

Built-in text editor (but emacs or vi or BbEdit can also be used).
Uses GCC as its compiler: compiling and linking many modules is very easy.
Support for ObjectiveCee, CeeLanguage, CeePlusPlus, ObjectiveCeePlusPlus, and possibly other languages as well.
Plays nicely, but is not wholly integrated, with InterfaceBuilder. This is a GoodThing.
Graphical interface to GDB for debugging.
Customizable build process: throw in your own build phases, be they file-copying, shell scripts, anything...
Ability to run command-line instructions from any text buffer. (This may be seen as a needless feature, but I'm not sure.)
Excellent interface for editing target, build style, and executable settings.

ProjectBuilder is a CocoaFramework application, written at NeXt long ago.

Superseded by ExCode in OS X 10.3 (Panther)