Aristocracy, Oligarchy, Plutocracy, Diarchy, Theocracy, Autocracy

Aristocracy: It is a form of government in a state where the nobles, the best citizens in a state, rule. It is the government of a few for the benefit of all and it is a form of oligarchy.

Oligarchy: Oligarchy is a form of government by a few people or a group of people.

Plutocracy: It is government by the rich, by the wealthy class. 

Diarchy: It is a type of government by two independent authorities. Power is vested in two rulers or authorities (it was operated in India between 1921 and 1937).

Theocracy: It is a government by a group of few religious leaders e.g. Vatican City, Afghanistan, Yemen, Algeria, Mauritania, Iran, and Saudi Arabia.

Autocracy: It is government by a person who has complete power over the state.