Zmanim is a free mobile application developed by Jay Gindin that provides location-aware Jewish prayer times and holiday start/end times. This app includes over 90 different zmanim, including GR'A and MG'A, which can be selected with a single click. Users can also manually select their location and time zone if the app is unable to determine it.

One of the standout features of Zmanim is the ability to set user-defined alerts for any zman, up to one hour in advance. Users can go to preferences and choose which zmanim they want to receive alerts for and how soon (zero to 60 minutes before). They can even choose the tone (if any) to play when the notification is displayed.

Overall, Zmanim is a useful and easy-to-use app for those seeking location-aware Jewish prayer times and holiday start/end times with customizable alerts.