The name is Roblox. You can register by only choosing username and password. No E-Mail required.

And there you can create worlds by using an map editor. Its all free and everyone can do it. You build the map, then you create the tokens (simply build an object), then you place them randomly or by putting them in, and then you let the coins show the private key which is loaded with skull.

So you have to konw how to build a map and a little bit how to code cause the private keys are only visible if you are nearby a coin. And a little bit coding to place the coins objects randomly. So someone who can code and has time to build maps can do this easily.

Only thing needed is access to all the coins cause you have to load the private keys which can be then found by people.