Social pressure (and proof)
Etsy will show a banner when there is limited stock of an item, but many people have it in their baskets.
To be clear, this is on the "social pressure" side of UX, and I wouldn't recommend it for everyone.
Many sites do this when it isn't true, and that's absolutely a dark pattern.
But, it's an interesting technique if you can dial in the right level of nudge (without being too manipulative).
Unlocking Amazon's joke
When reviewing items, Amazon will incentivise you to review more by offering to tell you a joke.
Creating a habit
After using Slack's "Catch Up" feature (and feeling "complete"), they'll prompt you to add the widget to your home screen.
Spotify prompting mixes
Occasionally, Spotify will show you your top genres, and prompt if you want a playlist mix created for you.
Dynamic event previews
When changing the default length of a calendar event, Amie shows a dynamic preview of that event using your current time.
Onboarding Aha! Moment
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).
Social pressure (and proof)
Etsy will show a banner when there is limited stock of an item, but many people have it in their baskets.