One that immediately comes to my mind is the 2008 Google Book Search Scratch and Sniff :D
Google Book Search has a new section allowing users to "scratch and sniff" certain books. Users are asked to "...please place your nose near the monitor and click 'Go'", which then "loads odors". When clicking on "Help", users are redirected to a page in a book that describes the origins of April Fools' Day.
I remember vividly how kids at my school were debating if the screen smelled or not. Such a fun and innocuous joke, I remember it with warmth:)
Bonboarding