Standard modal. Includes a close button in the top left so the user can dismiss the overlay.
Fullscreen modal. The user can dismiss the overlay with the close button or back button.
Modal without a dismiss button in the top right. This should be used where the user has to make a choice or confirm they've seen something.
O-overlay can also be used to create overlays that don't sit in the front centre of the screen but appear in a specific area.