Open Source

Apple, the first major computer company to make Open Source development
a key part of its software strategy, continues to use and release significant
quantities of open source software.

Bonjour

Bonjour, also known as zero-configuration networking, enables automatic discovery of computers, devices, and services on IP networks using industry standard IP protocols. It is a key component of Apple applications (e.g., iTunes and iPhoto), and devices (e.g., Apple TV and AirPort). Developers can easily leverage Bonjour from both OS X and iOS. View Downloads and Documentation

Java

Java

OS X offers a standard Java environment for running Java Applets through the Safari browser or for development with the complete Java Development Kit (JDK). The JDK is automatically downloaded and installed as soon as you try to run any software that depends upon Java. With support from popular open source IDEs such as Eclipse or NetBeans, the Mac is a great platform for running and developing Java applications.
View Developer Documentation

UNIX

UNIX

The most widely-sold UNIX operating system, OS X combines a fully-conformant UNIX foundation with the richness and usability of the Macintosh interface. View Developer Documentation

WebKit

WebKit

WebKit is the open source web browser engine at the heart of Apple's Safari web browser on Mac, Windows, and iOS. It also provides a system-level framework engine that powers Dashboard, Mail, and many other OS X apps. Webkit Open Source Project