Have you seen tmuxinator basically does same and also as screen background app.
Yea, that's a pretty cool one too. I like the send-keys feature, but don't know how often I would actually use it. For the most part, I needed something simple and haven't messed with tmux much. However, for tmux users, that would be a nice addition.
Syntax wise it so similar, few keywords here and there. I will keep on eye on mert.
Here my config example. It is vim for editor, rails api only and standard frontend.