Processby

<p>The plugin allows you to create and edit the robots.txt file on your site.</p>
<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!

bettoadami

<p>A Multisite Network plugin that removes the automatic sitemap link (deprecated practice) and adds custom parameters/lines at the end of the default Robots.txt whenever called. It will enable small adjustments for each site on the network – like pointing again to specific sitemaps if needed – without sacrificing the default conventions coded to WordPress’ core. To make the adjustments, look for a text area at the end of General Settings Page.</p>


Robots.txt Extender

Dynamic robots.txt for Multisite! Change parameters, or don't, for each site of your network without losing the defaults from WordPress Includes.

Robots.txt Editor vs Robots.txt Extender