About ArcGIS extensions
Extension products let you add more capabilities to ArcGIS. These specialized tools allow you to perform extended tasks, such as raster geoprocessing, three-dimensional (3D) analysis, and map publishing.
See Also:
How to use extensions3D Analyst
ArcScan
Data Interoperability
Geostatistical Analyst
Maplex
Network Analyst
Publisher
Schematics
Spatial Analyst
Tracking Analyst