ANARCHY
No government at all. The state between one constitution and the next, and the state a Republic or Democracy falls into when its cities riot too long.
It collects NO taxes and funds NO research. Treasury and laboratory both stand idle until a new government is chosen.
Revolution is the only exit, and it is not instant.
Corruption is ruinous — worse than under any despot.
The despot's tile penalty applies: any tile producing three or more of anything loses one.
No unit is supported free; every one costs its home city a shield. A settler eats one food a turn.
Martial law still works. Troops in a city quiet its citizens, which in anarchy is the only instrument of government left.