Neocron, a nano-tech sci-fi MMORPG, had a good system. You had a portable factory. (That could easily be replaced with a stationary blacksmith's forge.) You could find blueprints which detailed the parts required to build something. Many parts were quite common (eg. scrap metal) but others were quite rare. You placed the blueprints and the materials in your factory, hit go, and several minutes later - pop - a new weapon/tool/armour! It's a bit like the Dragon Armour quest, but with many more designs and possibilities.
