Twitter Scripter is an agent (or scriptable background application) which allows you access to the Twitter API directly from AppleScript.
Twitter Scripter has no interface, and runs in the background waiting for AppleScripts to ask it to do something, just like Apple's own System Events does.
With Twitter Scripter you can send Tweets and direct message, search Twitter, retrieve timelines of tweets, retweets, mentions and more, directly from AppleScript.
Twitter Scripter works with the Twitter Accounts defined in the Mail, Contacts & Calendars System Preference in Mac OS 10.8, so no complex authentication is required is your scripts.
To see how to use Twitter Scripter, check out these examples.