Apparatus allows you to write and execute PHP code directly from your WordPress admin area.
When your code generates errors, warnings, or notices they are indicated by icons appearing next to the line that generated them. Clicking on one of these icons will run a search (either google or errordatabase.info) for that particular error message.
Tab override allows you to use the tab key in textareas just as you would in a desktop text-editor or IDE. In otherwords pressing the tab key inserts a tab character rather than moving focus to the next form element. Tab override is also available as a stand-alone wordpress plugin: http://wordpress.org/extend/plugins/tab-override/ There is also a version for MediaWiki: http://tinsology.net/plugins/tab-override/
Only administrators. Use of Apparatus should be restricted to users who know what they are doing. Appartatus allows you to run arbitrary PHP code and can do serious damage in the wrongs hands. If you are a WordPress developer using Apparatus for testing and debugging it is highly recommend that you do so in a testing environment.
Donations are a great way to keep me in business. If you are an experienced developer and have ideas (and not just ideas for apparatus) feel free to contact me. There are several projects I'm working on that could benifit from some additional help.