This is a great idea. You can build your own online game! How might you use it in your classroom? Pshhh, who cares! You make your own games! No, really, I'm not sure that you could create a game for the states of matter or equivalent fractions, but you could use it to discuss cause and effect or the importance of planning. Or, treat it as an incentive.
Write it on your communicator: sploder.com.