What is Mechazilla, which caught Starship rocket booster mid-air for the first time?

SpaceX's 'Mechazilla' launch tower successfully caught the Starship rocket booster using its giant mechanical arms called "chopsticks" for the first time. The arms can be used to stack boosters and spacecraft and are designed to catch the booster mid-air on its return from space. SpaceX aims to use Mechazilla to prepare a rocket for take-off within minutes of its return.