High-speed update-aware storage used in our region server infrastructure; provides a good middle layer for storage of rapidly modified information. RethinkDB
Heavily used in front-end client scripting and backend infrastructure; we've been progressively migrating all our infrastructure to be written in C#/.NET Core. C#
We use Lua as our primary scripting language for third party developers - it's fast, the runtime can be quite small and fits into everywhere it needs to go - from mobile to web. Lua