own product · email reminders
One field, no account to sign up for.
You want to be reminded about something, but installing another app and making another account is a hassle. tolongingetin asks for one thing: write what you want to be reminded about. The email arrives right on time, and that is it.
Why it was built this way
A small example of the same way of working: strip away everything that can be stripped until one field is left. The hard part is not adding a feature, it is daring not to put in a sign-up page.