Are there any free online games that help teach the principles of macro economics?

Answer 1

Not really. The problem with simulating economy as a game is that in games, players control things; in real economies, the determinants of long-run growth (such as productivity or capital accumulation) are outside of policymakers' control. King of England had no say in when (or indeed if) Thomas Newcomen would build a steam engine, James Watt would improve it, and countless industrialists around the country (and later, the world) would adapt it for their needs...