4. In Sweden, and some other European countries (and China?) a lemonade stand works by person-to-person bank transfers, initiated using a mobile phone app. The Swedish one is called Swish, but I link to the Danish one [2] as they have an English explanation.
People really do use these apps for things like lemonade stands. I've seen an unattended garage sale, where everything was priced and a sign gave a phone number for payment.
It's also commonly used person-to-person, e.g. if a friend owes me for a spare concert ticket, part of a restaurant bill or whatever.
[1] http://i.imgur.com/Smkim6Vr.png
[2] https://mobilepay.dk/da-dk/Pages/The-story-in-English.aspx