Module Development API
One of the major design intentions of Titanium is to provide not only a powerful platform for building applications, but also an extensible and modular framework to extend it. From the ground up, Titanium itself is built on the same module framework.
The module framework is platform specific. While the conceptual design is similar between the platforms, the actual code is dependent on the underlying mobile platform.
Please see the iPhone Module Development Guide or the Android Module Development Guide.
Titanium Mobile Dev Center