Macros for Designing by Contract in Objective-C simplifies the process of using the Design by Contract software methodology invented and pushed by Bertrand Meyer. This involves creating a "contract" for each Object in your program that explicitly states the input and output ranges that the Object expects. The macros implement the pre- and post-assertions as well as invariants and references to "old" variables (the state of the variable before entering a method).
ViewPDF is an application to view and navigate in PDF documents. It is the successor of ViewIt, which was intended to be a universal preview application for GNUstep. Now, there is Preview.app that plays the role of a preview application, and ViewPDF is focused only on PDF documents. It uses PDFKit to render PDF content.
GNUSTEP Live CD contains a lot of software for GNUstep, a free implementation of the OPENSTEP framework (which is also directly used in Mac OS X as Cocoa). It includes excellent applications for RAD (GORM and ProjectCenter). The CD is available for i486, AMD64, Apple Mac PowerPC, and Sun UltraSPARC computers.