The MA Rainbow Forex Indicator is a free and popular MT4 indicator that is useful for Forex traders. It works by combining multiple Moving Averages (MA) with different time periods and colors to detect the trend. It can be used to identify reversals and support/resistance levels. The indicator is easy to use and can be used on any currency pair. It is also available for free, making it one of the most popular and widely used indicators among Forex traders.