In the past, the gold standard was widely used, and historically, there were various variations of it. The most famous form of the gold standard was the international gold standard, in which currencies around the world were pegged to a fixed value of gold, with the US dollar as the central currency. It was established in the Bretton Woods Agreement held in New Hampshire, United States in 1944 and ended in 1971 when the US discontinued the convertibility of the dollar to gold.

The key features of the gold standard are as follows:

1. Stability of value: The gold standard links the value of the currency to a fixed value of gold, so when the value of gold is relatively stable, the value of the currency remains stable as well. This provides a defense mechanism against financial uncertainties such as inflation.

2. Stability of exchange rates: In the case of an international gold standard, it provides stability in international exchange rates. Each country's currency can be exchanged for a fixed amount of gold, leading to minimal exchange rate fluctuations.

3. Limitation of gold supply: The gold standard imposes limits on the supply of gold, which restricts the issuance of currency. This helps prevent excessive inflation of the currency and maintains economic stability.

While the gold standard provided many advantages in the past, it is not widely used in the modern era due to its limitations and drawbacks. For instance, the gold standard can constrain economic expansion as it relies on the supply of gold to determine the growth of the economy and the issuance of currency. Additionally, the value of gold can fluctuate based on market factors, and countries relying on the gold standard would need to adapt to changes in gold prices.

In the modern era, most countries have adopted flexible exchange rate systems and utilize central bank monetary policies to manage their economies. These flexible monetary systems are better equipped to deal with the volatility of the economy compared to the gold standard.