Intention.js: Rewrites your HTML based on the user's context.

It goes way beyond what css and media queries can do. Imagine writing a media query for a slow-connection, large, high-resolution device in portrait mode, for a repeat, paid visitor, that moved the physical location of DOM elements as a result of the query.

What's "appropriate" depends entirely on what you are doing. Intention.js gives you really fine tuned control over how an element responds to different contexts, be it a width threshold, interaction mode, display resolution, could even use scroll depth or number of user's visits to the site.