Blackbird offers a dead-simple way to log messages in JavaScript and an attractive console to view and filter them. You might never use alert() again. You can add Blackbird to your page easily, simply download the files and place them on your server or in a local directory on your computer. And then Include blackbird.js and blackbird.css in your page. Blackbird is has been smoke-tested on Internet Explorer 6+, Firefox 2+, Safari 2+, Opera 9.5.

Open Source Javascript Logging Utility

Requirements: Internet Explorer 6+, Firefox 2+, Safari 2+, Opera 9.5
Demo: http://www.gscottolson.com/blackbirdjs/
License: MIT License