Blitzen is a computer program I wrote one day on a whim, and it's turning out to be pretty widely used.
Blitzen is a bot that connects to the AIM service, and uses the screen name 'Blitzen Agent'. Anybody can interact with Blitzen by sending him IMs following a certain syntax. You can get help on what commands he understands by checking his profile.
The basic purpose of Blitzen is to allow people to send IMs to buddies who aren't online at the moment. In other words, it's a sort of quick-and-small alternate email system. Blitzen will store the message (called a 'blitz') in its database, and when the recipient signs on to AIM, they'll receive a message that they have a blitz waiting, and can then read it via Blitzen Agent. This is a good way to send quick messages to your friends without going to all the trouble of an email, and it's the only way to reach someone if all you have is their screen name.
Feel free to add Blitzen Agent to your buddy list and use him all you like.