HIIT, high intensity interval timer, is a no frills timer for interval training routines. You may specify a number of seconds for each active period, a number of seconds for each rest period and, optionally, a number of seconds before the end of each rest period to warn of the upcoming active period giving you time to prepare.
HIIT does not require any special permissions or display advertisements. It does not upload your times to anywhere or track your performance overtime. Just workout.