Greg Winiarski

BlackBox is symfony like unobstrusive debug bar attached to the top of the browser window.
How can it help you with development: 
1. instantly inspect global variables (GET, POST, COOKIE, SERVER) 
2. debug both frontend and admin area 
3. executed MySQL queries and time it took to execute each query (useful for finding slow queries) 
4. profiler for measuring performance of your plugins and themes 
5. errors occurred when loading WordPress page

BlackBox Debug Bar

Immediate feedback on a great majority of errors. Added a conditional red background to the Errors, and with this modification I have never miss even a notice anymore.

Thank you very much!

Essential plugin in my developer toolset

BlackBox is a plugin for plugin and theme developers. It collects and displays useful debug information (errors, executed queries, globals, profiler).

Alley

Matthew Boynes

An add-on for the Debug Bar plugin that will log and profile remote requests made through the HTTP API. This plugin requires the Debug Bar Plugin.
This plugin will add a “Remote Requests” panel to Debug Bar that will display the:
<ul>
<li>Request method (GET, POST, etc)</li>
<li>URL</li>
<li>Time per request</li>
<li>Total time for all requests</li>
<li>Total number of requests</li>
</ul>
Optionally, you can add ?dbrr_full=1 to your URL to get additional information, including all request parameters and a full dump of the response with headers.

Debug Bar Remote Requests

An add-on for the Debug Bar plugin that will log and profile remote requests made through the HTTP API

BlackBox Debug Bar vs Debug Bar Remote Requests