Twitter and other microblogging services

What?

"Twitter is a service for friends, family, and co-workers to communicate and stay connected through the exchange of quick, frequent answers to one simple question: What are you doing?"

Wikipedia says Twitter has been described as akin to a web-based IRC client. Twitter uses the Ruby on Rails web framework.

Twitter messages may be tagged using hashtags, a word or phrase prefixed with a #, such as #beer.This enables tweets on a specific subject to be found by simply searching for their common hashtag, provided that the user has tagged his or her tweet.

The @ sign before a username, such as @example, is used to distinguish a reply directed at a particular user. A message preceded by the @username prefix can still be read by anyone, but is treated as directed firstly to the user in question

"In February 2009, the Australian Country Fire Authority used Twitter to send out regular alerts and updates regarding the 2009 Victorian bushfires. During this time the Prime Minister of Australia, Kevin Rudd, also used his Twitter account to send out information on the fires, how to donate money and blood, and where to seek emergency help."

Private information:

"Twitter may sell, transfer or otherwise share some or all of its assets, including your personally identifiable information, in connection with a merger, acquisition, reorganization or sale of assets or in the event of bankruptcy."

Many Twitter look-alikes, extensions

E.g. How to Create an RSS-Enabled, Micro-Blog with Twitter