Are there other practical means of 'slowing' down an aircraft, other than parachutes?
For an aircraft to fly, it needs forward speed. If you slow down an aircraft too much, it will stall and fall out of the sky. Airplanes are designed to not slow down. It's not "if a Boeing 737 is slowed down to 80 knots, more people will survive". A Boeing 737 has to fly at 130 knots minimum. If you want a machine that can, it's a helicopter.

Most crashes happen suddenly, e.g. approaching a runway while not paying attention to airspeed. It's not like "Hmmm, I think it's going to crash in 3 minutes, let's arm this system to minimize injury". It's like, "we're stable, runway ahead, everything's good......(terrain! terrain! PULL UP!)......oh sh!t ! Max power!!!". If the pilot can foresee the accident, most of the time he can avoid it altogether.

If you know well in advance you ARE going to crash, chances are the aircraft is completely out of control, spinning around and falling. In this case I think a large enough parachute will be effective.