As for myself, this year I discovered a programming language that suits my needs perfectly - Clojure/Script. Unfortunately, I don't get to use it professionally (yet), however I use it for my own projects with great joy. Using one programming language across the whole stack, while leveraging robustness of JVM on the back-end and vastness JS on the front-end is immensely empowering!
Previous year's thread (2018): https://news.ycombinator.com/item?id=18745763
I'm a professional Android engineer, and as for me: I learned Kotlin and use it at work every day, and so far I like it a lot. I also learned a little bit of iOS development with Swift. I also experimented with Flutter developing non-trivial "Hello world" apps, and I feel that it reduces a lot of friction that a lot of native mobile developers encounter.
What's your favorite tech in 2018?