Monitter - a Twitter search engine that shows results from three searches in three columns, it has a widget for your blog sidebar, and also limits searches within a km radius.
Phweet - talk to Twitter friends over the browser or mobile phone without having to reveal phone numbers. Type in your friends username and a message, and a Phweet URL will be sent, it will call you and you await for your friend to join in, you can invite others as well…see more.
Roomatic - a Twitter chatroom, join a room and enter a tweet, it will automatically live in this room. If you don’t include the word of the room in your tweet it will add it for you with a hashtag.
If you are participating via Twitter your tweet will only appear in the room if it has the term in the tweet that the room is based on eg. Gmail.
It’s like you are on a Twitter keyword search results page that auto-refreshes and you can tweet into that page.
TwitHire - a Twitter job board