A very large asteroid (>500km) would be a good attempt at 'shattering'. (much like how the moon formed, in theory) Otherwise, a "small" black hole or other cosmic-scale forces would do the trick. A near by blazar would easily sterilize the planet if it were aimed at us, but there are none such objects we have yet observed. (luckily)

The sun itself is easily capable of smearing Earth out, but the real question is "how?". Even a crazy CME aimed directly at Earth would barely be able to wipe out technology, let alone life. A close call with another solar system would definitely stand a solid chance of wiping out life as we know it, but it wouldn't necessarily be terribly quick.

It'd be very predictable in that we'd be able to see another solar system coming for decades/centuries/longer, and many changes would still be longer than a human lifespan (outside of the final 'kick' event, which could be over in a matter of weeks/months and leave the surface freezing and potentially devoid of much atmosphere).