The document summarizes the worst currencies of the past decade based on their exchange rates with the US dollar. The top three worst currencies were the Zimbabwean dollar at over 642 trillion to $1 USD, the Somali shilling at 35,000 to $1 USD, and Turkmenistan's manat at 24,000 to $1 USD. Many of these currencies weakened due to economic troubles, political instability, or high inflation rates in their respective countries.