This addon lets you cast ground targeting abilities with only one button tap instead of double tapping.
The ground target indicator appears while you hold the abilities key down and the ability is cast when the key is released.

Additionally you can select for each ground targeting ability, if it should be smart cast (one button press) or cast via two button presses (like the regular cast system).

With the Dark Brotherhood update, ZOS will add a quick cast option for ground target abilities. ZOS' quick cast option however will cast the ability immediately, so there isn't any targeting indicator.
This addon is a kind of hybrid between the new quick cast and the normal cast system as it will cast the ability with only one button press while still displaying the target indicator.

This addon works with the current live version of the game and with the Dark Brotherhood version on the PTS.