Eventtrack - build “on the fly” groups for Twitters at events, users can discover and follow people at the same event
Inner Twitter - receive tweets (chime messages) every 15mins, hour, etc…when you receive this tweet stop and meditate on the moment.
LoudTwitter - auto post tweets to your blog
Twibble - allows to send twitter updates along with your location via GPS
For other Twitter tools see my list.
If a Twitter tool has a Twitter account (makes sense), then follow the latest at Twtooltrack.