I'm really not sure if an app like the one I'm about to describe exists, but I think it doesn't. yet. Anyway, it's a running app where you can set a target diatance (eg. 2.4km) and set a targeted time to complete the distance (eg. 12mins). at every set interval (either distance or time eg. 100m or 30sec), the user will receive sound notification on how fast he's going at, wether he can achieve the targeted time or if he's too slow, etc. and in between notifications, give motovation to keep on running. just an app I'd pay to have. an app a lot of people would need to achieve such precise goals.