This is a tax on financial transactions, it is being discussed again at the G20 finance meeting as a way of cooling down the rapid high speed trading that characterises modern finance, as opppsed to the older invest and hold style of trading that stock markets were created for.
To me it looks like a good idea on the surface but will invariably go nowhere as the trading empires will not sanction it, but changing the economy from one driven by trading to one where we invest in innovations is a critical part of dealing with energy depletion.
Good idea, not going to happen.