I was confused, because i know one other ruby program called foreman.
Why confused? Overmind basically does the same thing as Foreman - runs processes from your Procfile. So maybe you have a web: and worker: process - Overmind will run them for you.
The difference between Overmind and foreman is that Overmind runs processes with tmux, which makes it a lot easier to interact with them. Plus there's lots of extra config that foreman doesn't have.
I was confused because there is https://github.com/ddollar/foreman and https://github.com/theforeman/foreman