Hi Hive account@andymandy - in short, most likely; an Amazon on EOS would look like a peer to peer exchange (think Ebay, or what Amazon has actually become with its sellers program) and a third party is already building a dapp along these lines.

Gmail doesn't have a strong use case for decentralization, and we can't confirm whether it's technically possible on EOS. Facebook could be facing stiff competition in 5 years.