- 
  
  Feathers, shells, beans, etc.
 - 
  
  Gems and precious metals.
 - 
  
  Introduction of money itself.
 - 
  
  Introduction of paper money, used together with coins and precious metals.
 - 
  
  Invented by Alfred Bloomingdale and Frank McNamara.
 - 
  
  Use of mobile phones to pay.