[cess11]

I'd say it's uncommon but you'll often use Elixir wrappers around OTP stuff or Erlang libraries. Sometimes there isn't a wrapper for the library you want so you'd just call into the Erlang library directly, which is much easier and "noob"-friendly than FFI:s usually are.

For sets it's usually recommended to use Elixir MapSet. There is a Queue-wrapper around the FIFO-queue in OTP as well. For fun and learning you can also implement your own queues, or things like process pooling around the tooling already available.