Zepto is great. It's a subset of jQuery, with a compatible API. Out of the box it provides the most common parts of the jQuery API surface, probably catering to 80% of uses. It has (very discrete) plugins to cover say another 10% of cases, and if you need anything beyond that you can just switch zepto to jQuery and everything will just work :)

Of course this means zepto is a lot smaller than jQuery. Zepto is 47k unminified [1], jQuery is 78k [2]

[1] http://zeptojs.com/#download [2] http://code.jquery.com/jquery-1.9.1.js

Looks like if you don't need the other features of JQuery you just use it and ignore it. Otherwise you can just swap it out with JQuery instead and not break anything. Seems like a strict subset.