Joren wrote a nice how-to on his experience building a jib arm. I am not sure of the technical name for this device, and neither is Joren, but I do know it looks like a good tool to have for any filmmaker.
I don’t know if the proper name is jib arm, boom, or crane. Like everything else in the world, there are at least three names for this. The basis for this design is a four-link system so no matter what the angle of the actual arm is at, the camera “basket,” as I call it, is always parallel with the ground. However, I designed a way to tilt the camera up and down, so you can get bird’s eye shots that change to be low angle shots, etc. Basically, I tried to anticipate any need I might have of a jib arm and make it as versatile as possible.
Make your own Jib Arm – Link