Founder of TinyLetter here. Cool article! Glad TinyLetter is still going strong & a successful acquisition for MailChimp.
And banking.
A huge 'value add' which has caught on is being able to send real-life money with no transaction fees to other people.
And treated in novel ways - 'lucky money' to send friends in your friend circles, paying for a taxi, utility bills, seeing a movie, train and plane tickets, etc.
Wish there was a better archive than the bits saved at archive.org.