Tenseg LLC

This plugin will look at another site you specify whenever a 404 error occurs and check if the requested path is there. If the path is found, it will redirect there rather than show the WP 404 page.
This is particularly useful to silently redirect over to an archival copy of a website when a major redesign has been done.
More information about this plugin can be found <a href="https://www.tenseg.net/software/404sitechecker" rel="nofollow ugc">on its homepage</a>.

404 Site Checker

When you get a 404 this will check the requested path at a site you define and redirect there if found rather than showing the 404.

latorante

This plugin takes care of WordPress inner comments error handling, and shows comment errors above the form, instead of using the weird grey page with single line error description. All this out-of-the-box.
It also remembers what you’ve typed in. So for example, if you fill in the comment form, and send it and forget required field, it will show the error above the form, and prefills the form with values you’ve submitted so you don’t have to retype them again (which is annoying).
By default, the plugin prints the error in this markup:
<pre><code><div id="formError" class="formError" style="color:red;">
 --error-here--
</div><div class="clear clearfix"></div>
</code></pre>
So it should be quite easy for you to style it in your css file with <code>".formError"</code> or <code>"#formError"</code>, you know the drill :). The default red colour is there just in case you won’t be able to style and since it’s error, red seems appropriate.
By the way, if you’ve customised your comment form with new fields, and you’re using the <code>preprocess_comment</code> hook, with the correct WordPress way of handeling errors, which is using <code>wp_die</code> on error encounter, this plugin will play nicely with that, and display your error messsage above the form as well.

404 Site Checker vs Comment Form Inline Errors