This is the Eclipse Class Star Destroyer from the Empire at War video game. It was the flagship of the resurrected Emperor Palpatine. It was even more massive than Vader's flagship, Executor, and in the game, it was armed with a superlaser, the "Eye of Palpatine," was was capable of cracking the crust of a planet (but not blowing it to smithereens.) And thanks to the movies, it's no longer canon. This model was constructed of roughly eleven thousand pieces.