Twitter Headquarters, San Francisco, United States

There are numerous tools for adding content, monitoring content and conversations including Tweetdeck, Salesforce.com, HootSuite, and Twitterfeed. Less than half of tweets are posted using the web user interface with most users using third-party applications (based on analysis of 500 million tweets by Sysomos).
Authentication
As of August 31, 2010, third-party Twitter applications are required to use OAuth, an authentication method that allows users to use applications without having to give the applications their passwords. Previously, this authentication method was optional, but now third-party applications that try to use a username and password will fail. Twitter stated that the move to OAuth will mean "increased security and a better experience."