A gadget is a small application or add-on that can be made available for easy access from the dashboard or the assets and navigation panes in Episerver. There are built-in gadgets both for the Episerver platform and product-specific ones, for example, gadgets for forms viewing, visitor groups statistics, version management and the product catalog, if you have Commerce installed. Developers can also develop custom gadgets to extend the features of your Episerver solution.
Gadgets are managed in a similar fashion both on the dashboard and in the panes in edit view. Click the Settings icon to access the gadget management options.
Select Add Gadgets, and select a gadget to add from the list of available gadgets.
For More Detail:http://webhelp.episerver.com/17-5/platform/managing-gadgets.htm