What kind of hot water system is this?

Based on what I see, the green pipe is the hot out supply to the house as that is on the output of the temperature mitigating valve. The green cap can usually be adjusted - some need pulling out to allow movement (a safety feature to prevent accidental changes), take care if you want to change the temperature though, a usual maximum is 46 deg C but often they are set lower like 42 deg C.

The pipe coming to that mitigating valve is the cold supply which also is connected to the bottom of the tank ie the supply point.

The pipe further back to the right is from the pressure & temperature relief valve so that the tank is not damaged due to an excess of pressure or temperature.