scribu

This plugin adds a dropdown with all the plugin author names. When you select an author, only those plugins remain visible.
Links: <a href="http://scribu.net" rel="nofollow ugc">Author’s Site</a>

Filter Plugins

Allows you to quickly filter plugins by author in the admin.

jamiebergen

Have you ever returned to a site that you built a while back and asked, “Why did I install this plugin?” This plugin provides an extra column on the Plugins page that enables you to add, edit, or delete notes about the plugins you have installed on a particular site. These notes are intended to provide documentation regarding why a particular plugin was installed and how or where it’s being used.
Features
<ul>
<li>Add as many or as few notes as you need for each plugin.</li>
<li>Edit or delete notes as desired.</li>
<li>Select an icon to go with each note to quickly convey what type of content it contains (e.g., info, warning, link, etc.)</li>
<li>Format notes using basic HTML tags if desired.</li>
<li>Any links included in the note will be automatically converted to <code>target="_blank"</code></li>
<li>Notes are added and updated via Ajax, avoiding slow page reloads.</li>
<li>Notes also display on the WordPress Updates page for any plugins that need to be updated.</li>
<li>A filter is provided if you would like to display notes beneath the plugin description instead of in a separate column.</li>
<li>A filter is available to selectively hide or display plugin notes in the admin.</li>
</ul>

Plugin Notes Plus

Very useful plugin to note why a certain plugin was installed on the site and any additional context around it, for other admins. Helps in housekeeping especially when there are more than one admins that try different plugins and forget to remove anything that is not wanted.

Super useful plugin for multi-admin sites

Does one thing and does it well.

I was about to build something like this and was thrilled this plugin not only existed, but is very well done! Thank you!

Exactly What I Needed!

Adds a column to the Plugins page where you can add, edit, or delete notes about a plugin.

Filter Plugins vs Plugin Notes Plus