For web dev, I would say stuff like Liveview / Hotwire. It makes you faster on developing complex web applications that would otherwise take much longer time w

For web dev, I would say stuff like Liveview / Hotwire. It makes you faster on developing complex web applications that would otherwise take much longer time with a traditional SPA-framework. You don't have to worry about handling server communications, how to send data and in what format etc, all updates will be handled in a consistent manner and it's scary easy to make live updates to all connected clients. Of course, these things are getting more popular now and a lot of people on HN may already know about it but I would assume most laymen still have no clue that this is a thing.