Given n blockchains with n >= 2, implement m >= n contracts (called twin contracts) in such a way that a transaction on one chain cannot take place without at least another mirror transaction on other chains. This pattern will continue to be documented at Twin Contracts Pattern
Given a fiat currency (like Euro), distribute a blockchain and offer exchange at the price offered by exchanges oracles for that currency. If you want to shadow Euro: you sell and buy this coin at the exact prices offered for Euro on Kraken and other exchanges. Make sure that the implementation is at least ERC20 compatible.
The blockchain needs a mechanism that stirs the shadow currency in much of the same fashion as a national bank: by selling or buying the coin in such a fashion that the price is kept in sync with the fiat currency. Keeping up with the market would not be hard if first a tick of one day is first resolved. If more computing power is available: before any transaction with external chains is performed: perform the price-fixing transactions. Ideally the commit of this group of transactions should take less time than a fiat currency exchange market tick.