ArcGIS Explorer is a free downloadable application that offers easy access to
online maps and GIS capabilities. Use it to combine free data from ESRI with your own data, as well as 2D and 3D Web services, to create custom maps and perform spatial analysis.
ArcGIS Explorer includes an SDK that supports developers in using the ArcGIS Explorer API to build tasks that plug into the ArcGIS Explorer application.
A task can be used to add a wide variety of functions to the standard ArcGIS Explorer interface, as it can execute any custom code. You could use a task to retrieve data or images from the Internet, query a remote database, perform a spatial analysis task on a remote server and extract information from the results.
You can also use a task to interact with the other classes in the object model of ArcGIS Explorer; for example you can find out information about the existing layers and results, run other tasks, add content to the map and search the features in local vector layers