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 expands the geodatabase functionality of the ArcGIS Explorer Desktop app.
It adds projections and geotransformations for use with ArcGIS Explorer Desktop.
GTP for ArcGIS the functionalities of ArcGIS to more than 90 raster formats.