[f5fstop]

Front is open, to prevent scuffing when in 4-wheel unlock driving, which the vehicle is in at all times until a lock button is pushed. The open differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force.
Rear is not posi; relies on TCS and E-locker on certain models.
The stab and TCS work on the brakes (the description from Beastmaster is pretty good), only main difference is the algorithms internal to the controllers. If no brake switch input, and there is slippage at a wheel, the TCS takes over, if the yaw sensor detects a skid, stability control takes over, if there is a brake switch, ABS takes over, and so can stability control under some conditions. Engine may also decrease torque by retarding the timing or shutting off injectors.