ImDisk is a virtual disk driver with several applications. It can create RAM disks, for instance; mount existing disk images as virtual drives; or create new images from scratch in just a few clicks.
Do you have a CD or DVD image, for instance - perhaps an ISO or NRG file? Just right-click the file, select "Mount as ImDisk virtual Disk", and the ImDisk dialog will appear. If you know what you're doing then there are a lot of configuration options here (you can set the drive letter, the virtual disk size, the image file offset, device type, whether the drive should be removable, and more). But if you're not too technical, no problem, the default settings are fine, just click OK and within a few seconds the image will appear as a browsable virtual drive in Explorer.
Maybe you'd like to create an image of an existing optical disc? That's equally straightforward. Right-click the disk, select "Save disk contents as image file", and the program will create an ISO image for you.
ImDisk isn't restricted to working with CDs or DVDs, though. It can also create and load images of removable drives. And it may be able to work with hard drives, too, although this gets more complicated (the program can't mount full drives, only partitions.)
Once you've finished with a virtual drive then you can usually remove it by selecting "UnMount ImDisk Virtual Disk" from the right-click menu in Explorer. But if you need more power then a Control Panel applet acts as a central point from where you can create, configure and remove your drives and images.
ImDisk's extensive set of command line options mean you can any of this (and a whole lot more) from your own scripts or batch files.
And the author's extreme attention to compatibility issues means you can install the program on any edition of Windows from NT 4.0 (no, really) to Windows Server 2008, on both 32 and 64-bit systems.