Just what is the device in the photos below? I traced the pipe it branches off of, and it is the gas line for the hot water heater in the house. (That pipe can be seen in the background of the end view.)
A flare fitting (male) with no female line attached (is the soft copper line loose -it's the type of thing this might mate to) a valve with the handle missing, an adapter to a larger pipe size, a short section of larger pipe, an adapter to smaller pipe size, perhaps a few more m/f size adapters tossed in there.
You didn't ask and I can't really divine a purpose for the short fat pipe. You could open it up and see if it's packed with some sort of filtering material - perhaps the thing that used to attach to the fitting was very picky about dirt in the gas.