The 140dev Twitter Framework is a free source code library containing a Twitter database server for gathering tweets for selected keywords, as well as a display plugin that lets you show tweets from the database in a single line of PHP code.
Hellotxt, the service that lets you simultaneously update your status and read your friends' status across many services, has now released an API. There is a long list of microblogging and social networking sites that Hellotxt interacts with, ranging from Facebook and LinkedIn to of course Twitter and FriendFeed (see their home page below).
The latest release of desktop Twitter app TweetDeck launched with a ton of new features, which includes showing geolocated tweets. If a tweet includes the location meta-data, TweetDeck shows a tiny marker icon. Click the icon and you get a map of the location.