Sound money must be intrinsically valuable, durable, stable, scarce, divisible, fungible, portable, and more. The bar is set high, as it should be.
In Liberty Minecraft players use diamonds as money. They can be obtained by mining ore, by searching chests in the world, by selling claim blocks, or by trading with other players.
The supply is fixed and predictable. All of the diamonds that can ever exist in the world are in the ground to be mined, hidden away in chests to be discovered and looted, or exist as claim blocks to be accrued over time.
Unlike in the natural world, these diamonds are easily divisible and fungible: each is just like another and can be converted into $1000 at the diamond exchange.
Diamonds are intrinsically valuable. They can be used to create the best armor in the game. Diamonds are also used when claiming land.
Claim blocks can be bought and sold at a fixed costs of 50 blocks per diamond ($20/block). When claiming land, a player will use their claim tool (a golden axe) and spend claim blocks.
Because players are awarded claim blocks over time, this makes our Diamond based money disinflationary, reaching an equilibrium point at some distant time when diamonds lost or spent balance with those found or granted as claim blocks through gameplay.
Edit: Our Diamond money is no longer disinflationary. Horray!