Six degrees of freedom (6DOF) devices allow for movement in three axes, tilt in two axes, and rotation in the third. Some of these devices look like small joysticks -- for example, the SpaceNavigator. These devices are typically used for computer-aided design and manufacturing (CAD/CAM) and other 3-D applications. With a new programming library, you can now also use them with Linux applications.
You might wonder why you would ever want to use such a device with a desktop application. Well, imagine using the rotation of the device to control your video playback speed, or moving the x-axis of the device to see the next image in a slideshow.
Sure you can map keys on the keyboard to increase playback speed 10% in a video player, and pressing Space will show you the next image in a slideshow viewer. But with a 6DOF device, moving the x-axis is not a binary operation. If you move the axis with more force, you should be able to skip through more images per second than if you move the device only 25% in the x-axis. For video playback you might want to move all the way to get playback to happen 20 times faster than real time. As soon as you let go of the dial you might want to revert to normal playback speed or paused video. You can makes the 6DOF device act in a similar manner to a jog shuttle.