How could no one mention emoneymail.
That was the one that started it all for me.
It was Chase's person to person payment service.
It was $1,000 a day for a $1 fee. I put the maximum on it every business day on a Chase credit card (no credit card fees) and transferred every day from one email (funding) to another of my emails (receiving). Lasted for a couple of years, then it just would not work any longer for me. No shut down notice - it just stopped working. There were a couple of others like it (as noted in a post above, c2it was one of them) during the tech boom, but they shut people down much faster (or just went away in the crash).