There are a lot of these game coins but they all have one big problem, the elephant in the room. The problem is that if the tokens are worth money than the game developer will take the tokens for him/her self. So imagine you've got a game, and you use this SDK which gives tokens to your players. what would stop you from playing your own game. If you as the developer play your own game then you can cheat and collect stuff for your self which you can then sell. the only way to stop this, is to charge the developer. this will stop the developer playing his own game and will also incentive him to make the game secure against cheaters but this means that if the game was to get hacked (people will be trying to exploit it) then the developer will lose tokens and his money.