Adobe Flash.

I don't care how many issues it has. It was the last tool that made creative web and game design possible without needing to be a full stack JS developer.

Part of the reason the web looks like a wasteland of responsive templates from 2012 is because the death of Flash changed how we wasted time on the Internet. Gone are the games and artistic experiences. In its place came content mills churning out GIF-laden quizzes, listicles and newsletters with a ton of ads littering every page. Buzzfeed is now a publicly traded company on the basis of how well it flattened Internet culture into it's one-size fits-all world.