A webpage with one million checkboxes. Checking a box checks it for everyone, in real time.
[update via Garbage Day: “Teens hacked One Million Checkboxes into their personal r/Place. Nolen Royalty, who made the website, coded a few features to limit spamming, but he didn’t anticipate a group of teen coders building a program that was only visible when converting the checkboxes into pixels or binary code, which they used to link to their Discord and post shirtless GIFs of Jake Gyllenhaal. Turning the site into a real-time rickroll just before it shut down”.]