Was wondering the same, the FAQ says:

  > What if I crash the drone?
  
  You can't! Our engineers have built in extremely robust   safety features,
  such as mid-air collision avoidance and advanced geofencing,
  that makes it impossible for you to crash our drones.
  You’re welcome to try to crash them :)

Does Cape allow independent control of the individual rotors? If so, I wonder how well the safety system would handle a drone being flown to its maximum altitude and then having the rotors on one side run in one direction and the other half of the rotors run the other way. In my mind this would cause the drone to rotate around a vector in the horizontal plane while gravity would be pulling the drone downwards. Higher altitude would give more time to build up the angular velocity of this rotation. If then the angular velocity is high as the drone approaches the ground, the system might not have time to recover stable flight. Thus the drone might crash.

Yep good point! We currently do not allow our users to actuate individual rotors to this degree of control. Instead, we allow lateral translation to move forward & backward, strafe left & right, ascend & descend, yaw the drone, and pitch the gimbal. Basically, standard WASD + mouse game controls.

Most quadcopters don't allow for the motors to be reversed - it's very rare for the motor controllers to support this unless the quadcopter is specifically designed for inverted / "3D" flight with custom motor controller firmware and bidirectional / 3D props.

"What motor inputs would cause the hardest recovery situation" is a pretty fun question, though - I think the best you could do would be to throttle the two motors rotating in a given direction to zero (both CW or both CCW), which would induce instability in multiple axes at once. But there's probably something more creative I'm not thinking about!

The obvious next question: where do I buy such an uncrashable drone for my own personal use? Is there something like that readily available on the market, or is that the company's secret sauce?

So, how exactly does this work? If I'm flying a real drone, in a real location, then how does your system stop me directly flying into a wall/into some other hazard at high speed?

Is it like a really advanced self driving car with sensors that detect solid objects and automatically steers around them?

Because with that quote from the FAQ, part of me wants to see the result of flying the drone full speed at every solid object in the vicinity. Or see how far it can go before the battery dies...