A timer app for iPhone that supports multiple, named timers as well as nested timers. Often, it's useful to have a warning or two before a timer completes. For instance, when taking an exam, it's nice to know when there is 15 minutes left, 10, and then 5 minutes left before the test is over. It can also be useful to receive warnings before your parking meter actually expires. Each timer in TimerStack can have up to 3 nested alerts, each set at user-specified times. TimerStack is also customizable with multiple themes, and supports Siri Shortcuts.