Rust - for low-level / systems programming
Elixir/OTP - for distributed systems, backend, JS-less
frontend (Phoenix LiveView)
Elm - for SPAs (Single Page Apps)
Julia - for number crunching
kdb+/q - for timeseries-specific workloads
Solidity - for get-rich-quick scams
NetLogo - for agent-based simulations
Typescript - for legacy browser, ReactNative and node.js code
Kotlin - for Android
Swift - for iOS and other Apple OSes