Elon Musk's SpaceX, which launched the biggest ever IPO, has overtaken Amazon to become the world's fifth most valuable company. The list is topped by Nvidia at $5.04 trillion, followed by Alphabet (Google) at $4.50 trillion, and Apple at $4.39 trillion. Microsoft stands fourth at $2.91 trillion, followed by SpaceX at $2.74 trillion. Amazon stands sixth at $2.65 trillion.