Quick Disk is a simple system utility that lets you eject volumes. As you may know, you can easily eject volumes from your Mac by going to Finder and finding the volume that you want to eject on the list of mounted volumes.
As you may also know, usually, your volume list will be full of DMG files and other disk images. This can be really annoying. Quick Disk makes the task of ejecting volumes much easier. It places an icon on the menubar. This icon shows how much space is used on your main hard drive. In my case, I was up to 97% of capacity. When you click on the icon, a window will slide down from the menubar. It will show all your mounted volumes, including of course the hard drives and any disk images. You can eject individual volumes by clicking on the "eject" button next to them, or click on "eject all" to eject them all at the same time. In my particular case, it would be a problem to eject all my disks at once, because I often use them. Still, being able to eject volumes from the menubar saves me a lot of time, especially when there are many windows open.
Quick Disk works like a charm, and you can customize how it displays your used space (in %, megabytes, etc).