Amazon Elastic Compute Cloud (Amazon EC2) is a web service that provides resizable compute capacity in the cloud. It is designed to make web-scale computing easier for developers.
Just as Amazon Simple Storage Service (Amazon S3) enables storage in the cloud, Amazon EC2 enables "compute" in the cloud.
This seems like the sound of the second shoe hitting the floor. Although I tried signing up for this as soon as I saw the email, I was already too late to get in on the beta and start playing. Maybe I'll get in on a second round.
EC2 seems a lot like User Mode Linux virtual hosting, but it charges
by the CPU hour by the hour of uptime instead of month-to-month. I'll be very interested to see how this shakes out, and what sort of web app architecture it encourages when used in conjunction with S3 - say AJAX-based queues for instance? - or if it just gets used as a straight LAMP host in general.