Modules

Here is a list of all modules:

QGIS core library	Contains all basic GIS functionality
QGIS gui library.	It's built on top of core library and adds reusable GUI widgets
QGIS analysis library.	Built on top of core library, the analysis library provides high level tools for carrying out spatial analysis on vector and raster data
MapComposer
QGIS network analysis library.	The network analysis library provides high level tool for build topology and analysis it
QGIS Server library.