Great question — answering as the UphillTech team:
There's the Nike+ iPod/iPhone app , which according to Nike : Nike+ has 5 million users. There are a number of Nike shoes that contain the requisite sensor/chip, and some third parties, such as Polar , have provided accessories that work with the Nike system.
Full answer by JW8: https://sports.stackexchange.com/a/46 (CC BY-SA 4.0).
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