This is a pure-JavaScript library that detects whether Flash is blocked on the current page due to a Flash blocking extension.

Enables <video> tags in all major browsers.

Reorder and filter items with a nice shuffling animation.

a JSLint server for more expedient linting

Firediff is a Firebug extension that tracks changes to a pages DOM and CSS.

Fast symmetric cryptography in Javascript

Uki is a fast and simple JavaScript user interface toolkit for desktop-like web applications.
It comes with a rich view-component library ranging from Slider to List and SplitPane.

Highcharts is a charting library written in pure JavaScript, offering an easy way of adding interactive charts to your web site or web application. Highcharts currently supports line, spline, area, areaspline, column, bar, pie and scatter chart types.