ArcGIS Explorer Desktop is a GIS viewer that gives you an easy way to explore.
ArcGIS Engine is a complete library of embeddable GIS components for developers.
It is a set of tools for ArcGIS that enable the users to create surfaces.
It adds projections and geotransformations for use with ArcGIS Explorer Desktop.
GTP for ArcGIS the functionalities of ArcGIS to more than 90 raster formats.