iamklaus

Whenever you use wordpress as somekind of a wiki or glossary, there might be some post that you would like to be informed about updates by others. This plugin adds the possibility to decide by each post on the frontend, if you would like to be informed by email if any updates have been on your post of choice.
The email you will receive shows in a comprehensive diff the changes of the old and new version.
<h3>Arbitrary section</h3>
<pre><code><?php code(); // goes in backticks ?>
</code></pre>

NotifyMe

Users can decide on the frontend to receive emails when a particular post has been modified.

AbroadPal

Notification Widget offers you the ability to insert and fully customize an overlay widget for your website, blog, etc.
You can easily change all settings of the entire overlay in the Dashboard. 
There are the following settings for you to change:
Overlay Style: 
– colors of bar and content frame background 
– text of the content frame and bar
Overlay Layout: 
– distance of the close button to the borders 
– size of the close button 
– height of the bar 
– height and width of the content frame 
– widget position (X- and Y-axis)

Notification Widget

Notification Widget is a overlay allowing you to get a individual overlay for your website.

NotifyMe vs Notification Widget