The government with unlimited power among the options provided is typically a socialist oligarchy. In this context, an oligarchy is a form of power structure where a small number of people or entities hold significant power, and if it is combined with socialist principles, it may lead to a concentration of power without checks and balances.
The other forms of government listed (unitary presidency, parliamentary system, and constitutional monarchy) generally have some mechanisms or frameworks in place that limit the powers of government and provide for a separation of powers or rule of law.