The Bit.ly Java library by Finn Johnsen interacts with the API functionalities of bit.ly, the URL shortener. It uses BitlyAndroid.java and no external jar. Just like this library, bit.ly offers additional development tools in more languages. Not supported by bit.ly, but useful to interact with the API.
At the bottom of many blog posts (including this one) and website entries you're likely to find a widget that allows sharing to social sites or emailing to a friend. ShareThis competes with other systems like AddThis and SocialTwist to give publishers an easy-to-install sharing method.
The article focuses on URL-Shortener APIs that appear in ProgrammableWeb's API directory. It includes Proofeditors.com and the popular Bit.ly API. Special features of the APIs include added security, special tools, and shortening for unique platforms. Also listed: 32 Bit.ly mashups.