If you’re starting multiple applications in multiple languages, continue using foreman! If it’s a tool that’s worked well for you in the past (and you have Ruby installed on your machine) there’s no reason to switch now.
If it’s all Elixir/Erlang things you wish to start I would ask why do you want to use more than one VM?
In the Ruby world I might create a new operating system process to perform some work concurrently, but with Elixir/Erlang I just add more processes to my supervision tree. Easier to manage, and more performant 
