DAEMON Tools Ultra is a virtual disk application for drive images and virtual RAM space. It lets you create virtual images from discs and files; you can also edit and burn image files to optical discs. Ultra version can emulate unlimited number of DT, SCSI, IDE, and HDD virtual drives. Present version has the ability to write bootable images to USB devices.
DAEMON Tools is also available in Pro and Lite versions. Pro version lacks features such as RAM disks, bootable USB device creation, and virtual hard disk support. Lite is a free version that can only be used to mount optical and VHD images.