What was the best onboarding experience you've had?

I'm curious what makes for an above-average onboarding experience... you know, that little thing that made you feel special, expertly explained something, or just left you thinking 'wow'. They don't come along often, but I know they are out there.

One of my favorites was Typeform. The interface was just so novel at the time (and really still is) and the setup just kept pulling me in rather than making it feel like work. I've heard that Superhuman has an amazing onboarding, but so far have yet to get anyone to tell me what it was that made it special.

So what do you think? What are some examples of onboarding experiences that left an impression for you?