Minecraft 1.12.2 mod that gives modpack authors the ability to add crafting recipes into a selection GUI that is triggered by right-clicking while holding the right items.
This could, for example, be used for clay recipes. Instead of manually arranging clay balls in a different way in a crafting table, it would be possible to make it so that you right-click with a spatula in one hand, clay in the other, and just select the clay item you want to make. Another use example would be forging. Right-click with a hammer in one hand, an ingot in the other, and select your desired toolhead.
You can add as many recipes as you want with CraftTweaker. The possibilities are endless.