JoshuaPack

Why choose this plugin?
<ul>
<li>404 pages not working? </li>
<li>Would you like to have a custom 404 page? </li>
<li>Would you like the 404 page to be a static page? </li>
<li>Do you need to have a WordPress CMS page as your 404 page?</li>
</ul>
This plugin does it!
This a rebel plugin that does not use WordPress’s 404 hook. It was developed for themes or plugins that cause issues with the hook itself.
For more information see FAQ page.

HTD 404

This plugin will simply allow you to point to a page to serve up if you get a 404 error. Also it marks it as 404.

digitalacornjp

Do you want to get rid of WordPress overheads? 
Let’s output static HTML and get rid of that overhead.
<ul>
<li>If you use “?” in the permalink, adjust it that use slash-separated.</li>
<li>You can select the pages you wish to output in the options screen.</li>
<li>Outputs static HTML to the level below the folder where WordPress is installed.</li>
</ul>
<a href="https://github.com/digital-acorn-jp/wp2html" rel="nofollow ugc">https://github.com/digital-acorn-jp/wp2html</a>
<h4>Usage</h4>
<ol>
<li>Click the WP2HTML link in the sidebar, go to the plugins page.</li>
<li>Set the options and the pages not generated, the pages to add.</li>
<li>Click the Save button.</li>
<li>Then you will see a list of paths in bottom of page. Check the paths.</li>
<li>Click the Genarate button.</li>
<li>Genarated the static HTMLs.</li>
</ol>

WP2HTML

This plugin reads the WordPress data and generate static HTML.

HTD 404 vs WP2HTML