Why hasn't it been done before?

Good question!

If it was so easy to create an alternative currency system, surely someone would have done it before.

Well, of course, there are literally hundreds of alternative currency systems in use across the world.

But to the best of our knowlege, none of these has the statut of being an "official" currency - backed by a government.

Things would change enormously as soon as this happened.

The reason why it's not happened before is that there are vested interests close to the banking system that will do everything possible to prevent a change to the current system. When Banks can siphon off 3-4% of GDP in interest charges on government debt every year, this gives them a very strong incentive to keep the system going.

One of the justifications for setting up the N-Euro system is simply to prove that it doesn't have to be this way.