So, imagine this.... Right-click with emeralds: You hold emeralds (a stack of 1-64) in you hand, and right-click. A virtual chest opens. It's got a label on top that says "The 1-Emerald Exchange", or "The 7-Emerald Exchange"; however many emeralds you were holding. In the top left corner of that chest, there's one of three things - a stack of emeralds the same size, a fire, or an item you put there before. If this is your first time opening the chest, it's always a fire. Other spots in the chest are filled with items that other players have put in. You can take these, but only by swapping them with emeralds - the same number of emeralds as you were holding when you opened the chest. Those are the only ways you can interact with stuff in there. How You Sell Things: To sell something, put it in that top left corner space. That's "your spot". If nobody buys it, it'll be there waiting next time you open the chest. If someone does, the emeralds will be sitting there waiting for you instead. How You Buy Things: To buy things, you just swap emerald for them, in the right number. Easy. Prices? That's what the "exchanges" are - if you click with one emerald, that's "buy and sell at one emerald". If you click holding two, that's "buy and sell at two emeralds". Listings? In each of the virtual chests, the most-recently-updated item gets slot 2 (slot one is your own item, remember), the next-most-recent gets slot 3, and so on. So, players that just throw something in and then go inactive, on a large server, will have their thing fall off the list eventually. What This Gives: Player-run buying and selling, online and off. No invisible money. No commands. No big signs. Just count, hold, click, done. (Oh, and, duh: If multiple listings in each exchange were desired, the whole top row of the virtual chest could be set up as "your slots". Then, each player could list up to nine things for sale.)
