NIB files are creted by a tool called Apple Xcode. Xcode is a software package that contains Apple Interface Builder, an application for designing and testing user interfaces. Apple Interface Builder is a graphical editor specifically developed for Ui designers.

NIB file stores all the resources for given interface project. Inteface Builder is commonly used for creating interfaces as it allow faster and easier developmnt compared to writting necessary code by hand. Since Builder version 3, XIB format is used instead of NIB.