Addresses is a GNUstep address book that consists of a full-featured address book manager application, a source-code compatible replacement for Apple's AddressBook.framework (for accessing and manipulating address data programmatically), a framework of view/editor classes that make it easy to use Addresses from your own programs, and a number of tools. It is easy to use by both users and programmers and can store almost all imaginable data, including multiple phone numbers, emails, and addresses, photos, AIM/Jabber/ICQ/Yahoo IM details, and notes. It supports drag-and-drop and integrates well with GNUMail.
DevelKit Framework is an GNUstep/Cocoa framework with tools for reading, understanding, and generating source code from other applications. Its goal is to allow applications to generate code from non-textual representation, such as diagrams or other kinds of descriptions. Example features: an ObjectiveC source reader and generator, a project builder class, source structure related classes (class, method, and instance variables), templates, a tool for automatically generating accessor (getter ad setter), dealloc and archiving methods (interface and implementation) for a given class, and more.
GNUstep is a cross-platform, object oriented environment composed of frameworks, tools, and servers (daemons). It is very similar to the Cocoa frameworks from Apple, and tries to maintain compatibility with Cocoa wherever it is desired and possible. The frameworks provide classes for containers, distributed objects, object archiving, file management, text system, font management, image composition, WYSIWYG PostScript graphics, and more.
JIGS (Java Interface for GnuStep) allows Java programmers to use the GNUstep libraries from Java, but it is more than a set of bindings for GNUstep from Java: it takes advantage of the fact that Objective-C and Java are very similar languages to make it possible to use Objective-C classes from Java using exactly the same API (and vice versa). Moreover, JIGS can generate automatically wrappers for your own Objective-C GNUstep libraries.
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).