rflickr is a Ruby implementation of the Flickr API. It includes a faithful reproduction of the published API as well as method encapsulation to provide more useful object mappings. rflickr features result caching to improve performance.
If you're looking to run a successful developer program, you should probably pay attention to Mathys van Abbe. He's the founder of Mobypicture (our Mobypicture API profile), which has just celebrated its 500th developer.
With Pokémon GO seemingly taking over the world as players walk around in search of the virtual creatures, one developer used the Watson Visual Recognition API to analyse screen shots of the app to locate nearby Pokémon, winning Best Use of Watson challenge at the AT&T Shape Tech Expo Hackathon.