TweetPony is a Python library for the Twitter API. It offers an internal model system to simplify methods when using an API call. Users can also manually connect to API for instances not supported by the models.
Check-in app Gowalla puts a fun twist on location sharing by helping its users discover wonderfully-designed virtual items that can be found, swapped, and dropped all over the place. Developer Ben Dodson used the Gowalla API to put together Wallabee Travel Edition.