The current Grid Overlay Widget allows you to quickly render an MGRS (US National Grid) using client-side resources in a web application, however it requires a developer with the ability to host the application themselves. The US National Grid is a necessary component to disaster response and public safety applications and needs to be deployed quickly and efficiently. In order to simplify time sensitive applications, the USNG Overlay Widget needs to be an AGOL hosted out of the box web app builder.
Here is a little background information for those who are unfamiliar with the widget:
Esri Overview -
http://solutions.arcgis.com/shared/help/solutions-webappbuilder-widgets/widgets/grid-overlay/
In action (Click Grid Overlay icon under the search box in the upper left) -
http://esri.github.io/solutions-webappbuilder-widgets/
sar usar publicsafety USNG