The Esri Twitter for Geoevent Java Sample Code by Esri demonstrates API interaction to interact with social tweets. Features include Twitter inbound adapter, Twitter inbound transport, and Twitter outbound transport.
It used to be you could change anything layered on top of a map, but you couldn't change the underlying map itself. Now you have several options for changing the color palette and the visibility of different objects that make up your base map. The options vary on the amount you can customize and how much work is required. But all three of these APIs can have you map scripting with style.
MapQuest has launched another API on top of OpenStreetMap (OSM), the Wiki-like editable map of the world. The new search service provides geographic search results for any data added to OSM, such as streets or landmarks. Of note, the MapQuest API provides the service without any API Key requirements or rate limiting.