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.
GTP for ArcGIS the functionalities of ArcGIS to more than 90 raster formats.
It is a plug-in that provides interoperability between AutoCAD and ArcGIS.