The G8 are the top countries in the world who are financially the strongest. Meeting together, mostly at the senior finance official level to sort out problems of money, trade and investment. But it soon became obvious that more had to be at the table for things to get done. A representitive at least for the African continent, South America,the Middle East, Central Asia and so on. So the G20 was formed.
Formation of the BRICS as an organization was another outreach attempt by China. But in recent years the "R" and the "B" aren't looking so good, so I think the BRICS organization won't be so much fun for China who is too busy trying to buy all the gas Russia can sell.