Alloy Forgery adds a multiblock alloy smelter, the Alloy Forge. In it's base configuration it serves as an easy way to increase ore yield, but everything is data-driven allowing you to add new forges and recipes as you please. These data-driven features are mostly intended for mod authors, especially because new forge types can only be added through other mod-datapacks.
By default there are three forge tiers, each with different fuel capacity and speed. They're all made from different stone-like materials, you can look them up on the wiki.
All controllers are crafted according to this pattern, with the outer ring of blocks corresponding to that controller's material. To construct a forge, simply follow the convenient guide above this piece of text using any combination of blocks that forge type supports.