FB, Amazon, Google etc currencies don't seem to be happening. I think it will be government currencies or something like Bitcoin.
Amazon has its own Managed Blockchain for currencies https://aws.amazon.com/managed-blockchain/ as well as a ledger https://aws.amazon.com/qldb/ along with a POW https://cointelegraph.com/news/amazon-patent-casts-light-on-... so I wouldn't exactly be surprised if they push out their own coin.
I don't think Google has made any big moves in crypto. Though if Amazon/FB really start pushing for their own coins I doubt Google wouldn't try something to compete on that market.
They are a bit neither one thing or another. Bitcoin is fully unregulated so you can use it in ways that governments would ban if they could, fiat is pretty much regulated (apart from cash in hand), but Libra etc combine the inconvenience of crypto with being subject to regulation.
Bitcoin is big because it's adopted and decentralized.
The same fears about Facebook is why their currency will not be trusted. I don't trust Amazon, but I do trust Bitcoin.