I worked on a web app that used AS3 and Adobe Flex for UI. It’s crazy to think about how powerful that framework was and it was twenty years ago now.

No, it was never right for public facing web sites but it shined making internal admins. HTML5 still hasn’t matched it.

EDIT: turns out Flex still lives on as Apache Royale: https://royale.apache.org/ wish I had an excuse to take it for a spin.