P259 sinks Vbat at no more than ~350mA, intended use is for driving relays and small lights (shift light etc).
Stepper 4 channels of push/pull 12v@1A, intended use is for stepper type idle control motors, also used for driving "smart" coils and external ignition amplifiers that need 12v drive.
INJ FET sinks Vbat at upto 14A with high voltage flyback intended for driving injectors, can be used for various solenoids: relay, idle controller, boost controller.
IGBT sinks Vbat at some silly current, intended for driving ignition coils, can be used for various solenoids (as INJ FET).
Logic drives 5v at very low current, designed fo driving IGBTs