Zepto is a minimalist JavaScript library for modern browsers

Zepto is a minimalist JavaScript library for modern browsers with a largely jQuery-compatible API. If you use jQuery, you already know how to use Zepto. While 100% jQuery coverage is not a design goal, the APIs provided match their jQuery counterparts. The goal is to have a ~5-10k modular library that downloads and executes fast, with a familiar and versatile API, so you can concentrate on getting stuff done…”

http://zeptojs.com/

via: http://blog.caelum.com.br/nao-use-jquery-no-seu-site-mobile-conheca-o-zepto-js