A machine that you set down, add mining pipes, power, ect. It then mines a 3x3 horizontal (or vertical, if you placed from above or below) in the direction you were facing when you set it down, and goes until it runs out of piping (it harvests everything as it mines, but the real point of it is to clear tunnels for large complexes/subways/strip-mining [though if you're using miners, they're probably more effective]).
To make it clear, the 3x3 is centered around the pipe as the center, and the path is created as the pipe drills outwards.