Drupal is a PHP/MySQL content management/blog/web journal package.
More and more corporate enviornments are using blogs as internal communication tools. Being able to post to a blog directly from Tasks makes it very easy to put up a quick post about something you are working on.
If you have it enabled, there is a small 'Drupal' button in the toolbar on the task Edit screen. Press that button and it will send the task to the Drupal bookmarklet. From there, you can make any edits you want and post it to your blog.