Liking a tweet with the right hashtag used to turn the heart into a custom animation, like the WWDC heart. These hashflags run for a short campaign, then X deletes them. This saves every one.
A small custom icon, and sometimes an animation, that X ties to a hashtag during an event or ad campaign. It shows next to the hashtag, and some campaigns swap the like heart for a custom animation. They only stay live while the campaign runs.
When a campaign ends, X deletes the files and the animation is gone. Nobody had a full list, so I started keeping one. It checks X for new ones and pulls older ones from the Internet Archive.
Built by @0x_ultra