Fullstack Elm with Lamdera (opens in new tab)

I've been using lamdera regularly for a over a year. Having a full-stack, one-language solution makes development so much more pleasant and efficient. https://minilatex.lamdera.app

Lamdera might be the best incarnation of "isomorphic" code I've had an experience with. Game logic shared in both frontend and backend (of course, backend has to validate everything as somebody could spoof the WebSocket connection), not going out of sync, types reused.

Also, one of two best experiences I've had with backends (I'm a frontend person): the second one was Dark language (http://darklang.com)