Elixir. The ecosystem has been steadily growing (and, more importantly, becoming more robust and mature) throughout 2018 with continuously improved tooling, libraries and frameworks. I'm excited for many of the upcoming things [1] in the Elixir world, and how those things can improve the way I build (web) software in 2019.

[1] For one example, https://dockyard.com/blog/2018/12/12/phoenix-liveview-intera...