Twitter (http://www.twitter.com) asks the one question:

"What are you doing?"

and you have 150 characters to respond.

You can respond via the web, through the AIM or other Instant Messager, or through your cell phone text messaging (SMS) to 40404.

So simple, yet so addictive! Of course, the obvious answer to the question "What are you doing?" would be, "Typing/texting a message to Twitter about typing/texting a message to Twitter", but that goes without saying.

Lots of fun. If you choose to have your Twitter-ings public, they show up on a "public timeline" that shows the last 100 Twitters. It goes fast. You get your 15 minutes of fame - perhaps only 15 seconds.

It's not quite Instant Messaging. It's not quite texting. It's not quite a chat room. It's not quite a blog. It's a new Web 2.0 creation that is growing in leaps and bounds and asks very little of you in return.

Truly, truly addictive. The newspapers are saying that Twitter will be the NEXT big thing, and it's already happening. -Ken, creator of Twitter Submitter, an "any browser" based HTML code allowing you to update your Twitterr in a different way. http://twitter.pbwiki.com)
http://twitter.com/simplify3