The travel site Orbitz has partnered with Google to show a virtual walking tour of the neighborhood around a hotel. You and I know it as the Street View API, part of Google Maps (our Google Maps API profile).
Forecast, the team that created the acclaimed iOS weather app Dark Sky, has created an API that brings its gorgeous weather data and display into any platform. As Forecast put it, they wanted to transcend their work with Dark Sky.
This article offers an introduction ipapi, a service that provides information about your website's visitors based on their IP address. Using the service, you can determine the customer's location, timezone, default language and currency and details about their network's organizational identity.