A small side project of mine, sprint pacer is an app for track and field coaches and athletes to calculate appropriate training times, given that athletes have specific goals.
Sprint Pacer removes the guessing that's traditionally been involved in track and field, whereby coaches indicate some percentage effort for athletes to run at, and athletes do their best to guess how fast that actually is.
Sprint Pacer is available on the Apple App Store and on the Google Play Store. It's a minimal app that has one job, does it well, and is simple enough for anyone to use.