ThunderBoltAS3 is a project mainly written in ActionScript, it's free.
Original source of ThunderBolt AS3
ThunderBolt AS3 is a lightweight logger extension for Flex 2-4 and Flash ActionScript 3 applications using Firefox and Firebug
For more information check out its wiki page "ThunderBoltAS3" at ThunderBolt's project on Google Code.
All source code are open source and licensed under the Mozilla Public License 1.1. http://www.mozilla.org/MPL/MPL-1.1.html
If you have any questions feel free to post these on its mailing list on Google Code.
Jens Krause // WEBSECTOR.DE
Have fun!
-Jens