Processby

The plugin allows you to create and edit the robots.txt file on your site.
<h4>Features</h4>
<ul>
<li>Works with multisite network on Subdomains;</li>
<li>An example of the correct file for WordPress;</li>
<li>Works out of the box;</li>
<li>Totally Free.</li>
</ul>

Robots.txt Editor

Lightweight and perfect for multisite installations.

But in documentation need to say where the option/editor is installed (Settings > Read options).

Perfect!

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.

Robots.txt Editor vs Robots.txt rewrite