Headspace nudges you into sharing your 30-day passes with a friend, at the same time as onboarding that component.
This might sound obvious, but the UX magic is subtle.
They're explaining where the "share" feature is, and drawing your attention to it. But also linking the "why".
i.e., you want to have someone to share this with, and here's 30-days to get them started.
When reviewing items, Amazon will incentivise you to review more by offering to tell you a joke.
After using Slack's "Catch Up" feature (and feeling "complete"), they'll prompt you to add the widget to your home screen.
Occasionally, Spotify will show you your top genres, and prompt if you want a playlist mix created for you.
When changing the default length of a calendar event, Amie shows a dynamic preview of that event using your current time.
During onboarding, Arc will encourage you to toggle adverts on a webpage on and off, to demonstrate the difference in experience (and the value they're adding).
Etsy will show a banner when there is limited stock of an item, but many people have it in their baskets.