This is an adjustable grill system from Ceramic Grill Store It adds a great deal of flexibility and functionality to the Big Green Egg. It's all stainless steel, so it should last forever.
Here is the basic rig, spider, and slide guide. The spider sits 2 inches into the firebox, you can put a 13 inch grill grate on the spider to sear steaks, or put on a pizza stone for indirect grilling.
Here is the 13 X 17 oval grid on the slide guide, this grate will slide at the top 2 positions on the Adjustable Rig.
Here is the Big Green Egg 18 inch grate sitting on top of the Adjustable Rig.
This a 14 inch pizza stone on the bottom crossbars of the Adjustable Rig. This is my preferred setup for indirect, it allows you to more easily remove the stone at the end of cooking if you want to go direct.
Here is the setup for pizza, the stone is on top of the Rig Extender, which puts the stone 7 1/2 inches above the fire ring. For pizza it's best to cook as high in the dome as possible.
Here is the setup for ribs, 2 racks on each of the sliding grids, here is where the slide really comes in handy, allowing for quick swapping of top grate and bottom grate.
One of my reservations about replacing the Weber Smokey Mountain with the Egg was the single grill setup. This addition, while expensive, solves the problem very nicely!
Here is the 13" Pizza stone I bought to use on the spider.
Fox Run 13" Pizza Stone
Here is the 14" Pizza Stone used to cook pizzas on top of the Rig Extender
Old Stone Oven 14" Pizza Stone