Create theme for mobile phones and tablets only?

I've been checking the docs but I only found a way to use different style sheet for phones and tablets.

Is there a way to create another different theme only for mobile phones and tablets? And I'm not talking about creating a "responsive" theme.

I would like to display different information and not only change the structure. And also, optimize the loading of the site removing unnecessary javascript files and so on.

Is there a proper way to do it? Or I would need to find my own way.