Vex : Vex is a modern dialog library which is highly configurable, easily stylable, and gets out of the way. You'll love vex because it's tiny (6kb minified...
Modest Maps | Home : Modest Maps is a small, extensible, and free library for designers and developers who want to use interactive maps in their own projects.
Styletron : Styletron is a universal CSS-in-JS engine built from the ground up for high-performance.
jsfx : This is a javascript library (with frontend) for sound effect generation.
Headroom.js is a lightweight, high-performance JS widget (with no dependencies!) that allows you to react to the user's scroll.