Marc3842h uses Rust
Rust is used in Shirogane (https://github.com/Marc3842h/shirogane).
Shirogane is a osu! beatmap mirror built for shiro. We use Rust because of memory safe but still low level and high performance.
Provide Booking uses Elixir
Huge boon to productivity when coupled with Phoenix. Moreover, it has made background jobs and all the unseen aspects of a business easily abstracted.
Tinkhaven uses Haskell
Backend logic (REST, Auth0, Redis, Postgres, functional graph library (fgl), ...)