Dan,
> I was wondering what bug tracking software is used by
> http://bugs.mysql.com/, and if it also available open source? It
> appears to be the same package used by the PHP project
> (http://bugs.php.net) and the PHP PEAR project
> (http://pear.php.net/bugs/).
>
You can find the source for the software which bugs.mysql.com is based on at
the following URL:
http://cvs.php.net/php-bugs-web/
However, the source that you find in there is the one used by bugs.php.net.
Anyway, hope that helps.
--Joao
