Cocoa
The Cocoa environment
provides an advanced, object-oriented API for Mac OS X that makes it
easy to create complex applications using very little code. The secret
is in the power of the Cocoa frameworks themselves: they provide
enormous amounts of useful functionality out of the box so that
developers can focus on writing the code that’s specific to the domain
of their application.

Carbon
The Carbon environment
provides fine-grained procedural APIs in C and C++ that are intended
for developers who are migrating applications from classic Mac OS to
Mac OS X. Carbon applications can run on Mac OS 9 as well as Mac OS X,
making Carbon a logical choice for those developers whose applications
need to run on both systems.

Cross Platform
For cross-platform desktop application development, Apple supports two environments:

The
principle cross-platform API on Mac OS X is Java 2, Standard Edition.
Mac OS X version 10.4 "Tiger" provides both Java 1.3 and Java 1.4.2
integrated into the system. (Java 1.5 is also available as a developer
download; see the ADC Java
page for more information.) In addition, Apple provides the full JDK
for both Java 1.3 and 1.4.2, as well as implementations of Java 3D and
Java Advanced Imaging for JDK 1.4. Most existing Java applications run
well on Mac OS X without any modification, but some developers like to
take advantage of the unique integration that Apple provides with Java
in Mac OS X to make the user experience close to that of a native Mac
OS X application.

If you need for your application to run
on Linux or a UNIX platform other than Mac OS X, you may wish to take
advantage of Apple’s highly-optimized X11 implementation. Apple
provides a full X11 SDK as an optional install with the Xcode Tools.

XCode
Apple even provides the advanced Xcode Tools software development
environment free of charge with every copy of Mac OS X so that you can
start building great applications as soon as you get your Mac.

Xcode 2.1 is Apple’s tool suite
and integrated development environment (IDE) for creating
Mac OS X Universal Binaries that run natively on PowerPC and Intel-based Macintosh computers.
The IDE provides a powerful user interface to many industry-standard
and open-source tools, including GCC, javac, jikes, and GDB. Xcode is
designed to fully support the Carbon and Cocoa frameworks and Java.
It contains templates for creating applications, frameworks,
libraries, plug-ins, Java applications and applets, and command-line
tools. Developers can use Xcode to construct a user interface, test
code performance, and perform many other common development tasks.
For the latest Xcode release information and other details, see the
Xcode Updates page.