twython is an actively managed python wrapper for the Twitter and Twitter Streaming APIs. All functions are mapped to the coinciding endpoint in the Twitter docs, providing developers with a lot of flexibility.
The most popular Twitter ranking service, Klout, has used its API platform to boost its growth. The company, which is also expanding outside of Twitter, saw calls to its Klout API more than triple in just a few months. The company is now clearly in the API billionaires club.