michaeltyson

Leon Stafford

Save your visitors from unhelpful 404 errors!
Instead of quickly giving up when a visitor reaches content that doesn’t exist, make an effort to guess what they were 
after in the first place. This plugin will perform a search of your posts, pages, tags and categories, using keywords from the requested 
URL. If there’s a match, redirect to that content instead of showing the error. If there’s more than one match, the 
404 template can use some template tags to provide a list of suggestions to the visitor.
See the <a href="http://michael.tyson.id.au/smart-404" rel="nofollow ugc">Smart 404 homepage</a> for more information.
<h3>Template tags</h3>
<code>smart404_has_suggestions</code>
Returns true if there are some suggestions, false otherwise
<code>smart404_get_suggestions</code>
Retrieve an array of post objects for rendering manually.
<code>smart404_suggestions</code>
Draw a list of suggested posts.
Pass the parameter “list” to render suggestions as a list.
<code>smart404_loop</code>
Query posts for use in a Loop. Eg:
<pre><code><?php smart404_loop(); ?>
<?php while (have_posts()) : the_post(); ?>
 <h2><a href="<?php the_permalink() ?>"><?php the_title(); ?></a></h2>
 <?php the_excerpt(); ?>
<?php endwhile; ?>
</code></pre>
Note that the loop will not display pages correctly, as it is not built to support them. It is recommended that if you use 
a loop like that above, do not enable searching of pages.
<code>smart404_get_search_terms</code>
Retrieve an array of search terms used to populate the suggestions list, for use with contextual highlighting, etc.
For support and latest source code, please visit https://github.com/leonstafford/smart-404

Smart 404

Automatically redirect to the content the user was most likely after, or show suggestions, instead of showing an unhelpful 404 error.

devoutpro

NoMore404 is a free WordPress plugin for redirection of 404 pages and simple firewall to block malicious hosts and URLs. 
All redirections are done via 301 redirection. 
You can mark any hosts and URLs to be blocked as malicious as well.

Nomore404 404 Redirection and Firewall

NoMore404 is a free WordPress plugin for redirection of 404 pages and simple firewall to block malicious hosts and URLs.

Smart 404 vs Nomore404 404 Redirection and Firewall