Algorithus

This plugin allows you to easily control whether search engines are disallowed from accessing the root directory of your WordPress site by modifying the robots.txt file. You can enable or disable this functionality from the “Reading” settings page.

AWP Disallow Root Control

Disallow access to the root directory via robots.txt with an option to enable or disable.

Eugen Bobrowski

Plugin provide to help search engines to indexing site correctly.
A simple plugin to manage your robots.txt. Plugin donn’t create the file or edit it. This plugin edit WordPress output of robots.txt content. And get you a easy and usable interface to manage it.
Features
<ul>
<li>Drag-n-drop robots.txt paths</li>
<li>Changing <code>blog_public</code> option form plugin settings page</li>
<li>Site map field for robots.txt</li>
<li>Robots.txt physical file checking.</li>
</ul>

Robots.txt rewrite

first review

Provide the easy managment of your robots.txt from admin side. It propose you the advanced then standard robots.txt content too.

AWP Disallow Root Control vs Robots.txt rewrite