Five years ago Paul Rademacher reverse engineered Google Maps to put Craigslist homes and rentals on a map on his site. The site essentially pre-launched the map mashup category, because there was no Google Maps API at the time. Now it is the prototypical example and still used by many to find their new homes. And, of course, Google Maps is now by far the most popular API to use.
The Google Maps API took a hit in France as non-competitive. The Gnip API now lets its customers go back in time, tweet-wise, retroactively tracking specific terms. Plus: APIs for hustlers, putting the "why" in user permissions and 10 new APIs.