The 2008-2009 Recession wasn't that long, but it was one of the more significant downturn in recent time. During this time period, the Federal Reserve :
1) used open-market operations to purchase mortgages and corporate debt (i.e. quantitative easing), just as it frequently does even when the economy is functioning normally.
2) took the unusual step of using open-market operations to purchase mortgages and corporate debt, referred to as quantitative easing.
3) explicitly set its target rate of inflation at zero.
4) explicitly set its target rate of inflation well above zero.