Re4DeR

This plugin is very usefull if you want warn people going to one category.
It set cookie, co visitor will see alert message only once.
For example you have a magazine and in one category you have adult content. 
With this plugin you can set up warning for access to this category-and user have to confirm your message.
<h3>A brief Markdown Example</h3>
Ordered list:
<ol>
<li>Choose between alert and confirm</li>
</ol>

WP Warning

This plugin allow you warn visitors when they want to go in category.

vmihailenco

airbrake

benarent

This plugin collects and aggregates all errors created by WordPress and it’s plugins. It de-dupes and lets developers know how to fix issues fast.

Airbrake

License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html

Airbrake is collects all errors created by Wordpress and it's plug …

WP Warning vs Airbrake