Microsoft's Outlook blog:
So today, we're introducing a preview of Outlook.com. We realized that we needed to take a bold step, break from the past and build you a brand new service from the ground up. You already know Outlook via the Outlook desktop application-for PCs and Macs-as the world's most popular application for reading email, managing a calendar, and connecting to people. And you may have used the Outlook Web App connected to Exchange Server in your organization. Now, in addition to a desktop application and a service for businesses, we're offering Outlook as a personal email service - Outlook.com.