Ben Doherty (Oomph, Inc)

Specify a list of tags to keep hidden: These tags will be invisible to users, 
such as in tag clouds or in post tags lists. This is useful when using tags to 
control behavior of your blog, or when you wish to maintain groupings of posts 
out of the public eye.
This does not prevent tag archives for hidden tags from being accessible, only 
hides tag links from tag lists and tag clouds.
Capable users (with the see_hidden_tags capability,) can see hidden tags in 
tag lists (but NOT tag clouds.) Hidden tags will receive the .hidden-tag class 
and are grayed out by default.

Oomph Hidden Tags

Hide certain tags from tag lists and tag clouds. Allow capable users to see hidden tags with the see_hidden_tags capability.

DCoda

This plugin is only supported on PHP 5.2 or greater.
 
Black out certain words that may appear in a post especially when quoting. 
Aids you to keep the original content intact but maintain privacy or a family rating. 
Also allows the ability to hide explicit content, or spoiler information, such as sports results 
and film endings but allow the user to choose if they wish to view it.
Redactor gives you two forms of censorship:
1. Hide and Reveal
By wrapping a phrase in either [censor][/censor] or [spoiler][/spoiler] bbCode tags you will block out the phrase, but give the user the option to reveal the hidden phrase by moving over the phase with the mouse.
2. Automatic Predefined
On the <code>Settings->Redactor</code> admin page you can build a list of phrases you wish to censor. There are three types of possible censorship:
1. Blackout
This will remove the phrase from the post replacing it with black bars representing each word in the phrase.
2. Censor / Spoiler
This will obscure the phrase with either the word <code>Censor</code> or <code>Spoiler</code> but it gives the reader the opportunity to reveal the censored phrase.
3. Swap With
The most subtle form of censorship depending on how you use it. The censored phrase will simply be swapped for your desired replacement.
Redactor will match the phrases to be replaced to whole words and you will not have the problem of an accidental match inside a word, making nonsense of the post. 
Also for added safety Redactor will ignore any HTML or BBCode tags in the post, replacing only their inner content and not messing around with their attributes. 
To allow for the possibility that you may add phrases that overlap, you can prioritise the phases.
As Redactor filters the content each time the post is requested, It is recommended that you consider installing a page caching plugin. 

If you are having trouble and cannot find the answers in the <a href="http://redactor.dcoda.co.uk/help/faq/" rel="nofollow ugc">FAQ</a> you can post your support questions to the <a href="https://wordpress.org/tags/redactor" rel="ugc">WordPress Support Forum</a>
If you find Redactor useful please rate it at <a href="https://wordpress.org/extend/plugins/redactor/" rel="ugc">wordpress.org</a> and please consider making a <a href="http://redactor.dcoda.co.uk/donate/" rel="nofollow ugc">donation</a> to help us set aside more hours to maintain Redactor
Redactor is written by <a href='http://dcoda.co.uk' rel="nofollow ugc">dcoda</a>
You can check out our other plugins <a href="https://profiles.wordpress.org/users/dcoda/" rel="nofollow ugc">here</a>
If you require a custom plugin you can contact us <a href="http://dcoda.co.uk/contact/" rel="nofollow ugc">here</a> and maybe we could write it for you.
<h3>Copyright</h3>
(c) Copyright DCoda Limited, 2007 -, All Rights Reserved.
This code is released under the GPL license version 2, available here:
<a href="http://www.gnu.org/licenses/gpl.txt" rel="nofollow ugc">http://www.gnu.org/licenses/gpl.txt</a>
There are so many possibly configurations of installation the plugin can be installed on we limit testing to a PHP 5.2+ Linux platform running the latest version of WordPress at the time of release but it is released WITHOUT ANY WARRANTY; 
 without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Oomph Hidden Tags vs Redactor