Within a given voltage/current range the circuit on the right acts exactly like a capacitor with a negative value. The value can be adjusted by changing the 1k resistor.
The opamps with a gain of 1V/V are differential amplifiers http://everycircuit.com/circuit/5474894897479680
Note: the capacitor can be replaced by any component you want a negative equivalent of such as a resistor, inductor or diode.
