Brad Williams

This plugin lets you create category mappings allowing for one top-level blog to act as a portal for your global community of WPMU blogs. Category postings are aggregated based on the mappings and displayed on the top-level blog.
Features:
<pre><code>* Map multiple top-level categories
* Built-in sidebar widget to display all categories
* WordPress MU 2.7 approved!
</code></pre>
<h3>Plugin Support</h3>
<a href="http://webdevstudios.com/support/wordpress-plugins/" title="WordPress Plugins and Support" rel="nofollow ugc">WordPress MU Category Mapping Plugin</a>

WordPress MU Category Mapping Plugin

Plugin links categories network wide to provide one top-level blog to act as a portal for your global community of blogs

oltdev

This plugin aggregates multiple blog(s) into one 
single blog. The imported blogs must be in the same WPMU installation 
as the destination blog. Suitable for WordPress MU only.
<h3>How to</h3>
<ol>
<li>
Using your favorite text editor, create a .txt file with all the 
links of the blog you wish to import. Separate each blog in new line. 
You can name it anything you want. Here’s an example.
https://wordpress.org/blog1/ 
https://wordpress.org/blog2/ 
https://wordpress.org/blog3/
</li>
<li>
From the menu you can choose to specify categories and tags filter. 
You can have multiple filter in one line. They are comma seperated.
</li>
<li>
Click on import button and begin the import.
</li>
</ol>

Multiple Import

Aggregate multiple blog(s) into one single blog.

WordPress MU Category Mapping Plugin vs Multiple Import