ArcGIS is the most common GIS software in North America.
The main components of the suite are -
Accessing, managing, and creating GIS data and metadata.
Data display, analysis and communicating results via map products.
Data conversion, management, processing, and analysis. ArcToolbox is accessed from within either ArcCatalog or ArcMap.
Data collection software for GPS-capture and digitizing.
3 different levels of licensing are available: ArcView, ArcEditor and ArcINFO, in increasing order of functionality.
To determine which level licensing is installed, in ArcMap or ArcCatalog choose, Help / About.