As rumors continue to swirl around LinkedIn's possible IPO, the professional social network is steadily adding useful features that help transcend the platform's technology into other applications. LinkedIn recently launched two-way integration with Twitter and also rolled out a plug-in to pull in your LinkedIn contacts within Microsoft Outlook. And today, LinkedIn is opening up its API to start letting developers make applications that tap into LinkedIn's social network. While LinkedIn is releasing 11 different APIs, they fall into three distinct categories. First, developers will be able to let users easily access their information, profiles, connections and messages via oAuth login. The second functionality is to give users the ability to make actionable decisions about information, but letting them message their LinkedIn contacts, post updates, accept contacts and more. And the third piece of the puzzle is search. So developers will now be able to embed LinkedIn search in other applications. The social network's search engine was re-launched last year and has done over one billion queries in this year alone.