Windows Live SkyDrive is Microsoft's free Web storage service. Users get 25GB of space in the cloud where they can safely keep their files, and they can log in to access those them with their Microsoft Live ID.
One of the things that makes SkyDrive neat is the desktop integration. Windows users who are running Internet Explorer can run a special SkyDrive-specific ActiveX control that lets them drag and drop files from their desktop to upload to their Web storage. SkyDrive is also beginning to be integrated into other Windows Live services like Spaces, which means users can have a central repository of files and access them from any of Microsoft's online services.