A while back, Euphoria made an alternate currency system, and an alternate currency shops system; he had planned on releasing a third script to complete the set, enabling players to convert between the alternate currencies. However, he was unable to get around to it, and the idea kinda just fell away.
So, what I've done is made a common event system that allows you to convert between the standard game-currency and three alternate currencies. The system I'm sure can easily be expanded upon, but this is a decent starting point for those who might want to use it. The demo has both the alternate currency script (required for the demo to work) and the alternate currencies shop (not necessarily required, but good to have if you want to use the demo to make a game from).Download Here