I've always been curious if they can reproduce the NFC style wallets in Japan (Asia?) in the USA.
Here in Japan the train companies have NFC cards. The cards act mostly as cash. You put money on the card itself. I don't know exactly how the accounting works but AFAIK there's no server being contacted when you make a purchase. The system some how instantly deducts the money from your card and updates your history on the card.
This makes them super convenient unlike stuff like Square Wallet or even Google Wallet. You tap the card/phone on the machine and you've paid in under 1 second. No need to press anything, type any passwords, nothing.
The chips were later added to feature cell phones around 2006 so you could tap your phone instead of a card. You can also add more cash on them from your phone. Some Japan only Android phones also have them. Of course iPhone does not.
Trains, busses, many taxis, vending machines, convenience stores, some restaurants have the readers next to their registers.
Transactions are stored on the card and many laptops in Japan have built-in readers. My 2006 Vaio did. Touch your card to some spot on the surface of the laptop and get instant expense report for work/taxes. You can add credit to the cards on your laptop as well.
I have no idea how they prevent fraud given they can be updated locally (filling them with money without going through the proper channels). As for theft, scanning people as they walk by, they do seem to need to be within 1cm or so to read/update. I haven't looked into it though. On the other hand they aren't tied to any other money meaning they're basically like carrying cash. If you lose it all you lost is your money on the card and your purchase history. There's no "account" and it's not connected to any bank or credit card so the damage is minimized.
I have no idea if those would go over anywhere in the USA except maybe NYC, Chicago, SF. They arguably work in Japan because so many people commute so even if you never purchase anything they're super convenient for commuting (no need to buy tickets). Once you have one they end up being convenient for other things.
At the same time, I don't see anything less ever taking off in the USA. Google Wallet etc aren't more convenient than credit cards. Felica cards are.
I realize I think in SF the Clipper card and in London the Oyster cards are the same tech? But I don't think either can be used for anything other than trains/busses.
Also the chips don't need batteries so even if your phone battery dies you can still pay with the chip in your phone.