lukaiser

ILAnnotations allows you to select a text in a blog post and add your comment to it. 
The plugin uses the standard comments engine of WordPress, so all other comment plugins should work just fine with it. 
Shortcodes are used to mark the highlighted text. This allows you to still edit a post and move stuff around without losing the annotations.

ILAnnotations

Annotate any text in a blog post and add a comment to it.

cloudknight

Colorful Notes TinyGlow Annotator lets users highlight any text and attach color-coded notes directly to your content. Admins can respond to each annotation individually, keeping feedback organized and easy to follow. Ideal for collaborative writing, educational platforms, and community-driven engagement.
Features:
<ul>
<li>Multi-section text editor with independent styling</li>
<li>Text highlighting and note-taking</li>
<li>Admin can reply to user notes</li>
<li>Users can reply to admin responses</li>
<li>Color-coded notes for easy organization</li>
<li>Role-based permissions</li>
<li>Note length validation</li>
<li>Clean, modern interface</li>
</ul>
Pro Version Available:
Upgrade to Colorful Notes Pro for advanced features and premium support.

Colorful Notes TinyGlow Annotator

Add colorful, interactive notes to any text on your WordPress site with an elegant interface.

ILAnnotations vs Colorful Notes TinyGlow Annotator