Elixir
Functional language on the BEAM (Erlang's VM) — José Valim, 2011. Modern syntax + macros, all of OTP's concurrency and fault tolerance.
Pattern matching, immutable data, the pipe operator (|>), GenServer, supervisors. Scales smoothly to millions of lightweight processes. The Phoenix web framework is the default; LiveView (server-rendered reactive HTML over WebSocket) is its unique selling point.
Powers Discord (chat), Pinterest's tag service, Bleacher Report, the Heroku CLI. Sweet spot: real-time, high-concurrency services. Less adoption in data-center-heavy AI/ML stacks where Python dominates.