true Google 404 is a free wordpress plugin that adds functionality of displaying a list of related links on your website when a reader encounters a 404 error. It transforms your standard “We can’t find that” to “Maybe one of these is what you are looking for” and displays a list of related links with some description.
This keeps your readers involved in your site and does not irritate them when they encounter a 404.
true Google 404 uses the trueGoogleSearch API (again, created by me) and intercepts your standard 404 page and returns a list of links with appropriate anchor text and short description which will help your user to find the content they are looking for.
You can limit the search to just the content on your site, set a default prefix to the search query (for example in case you want to limit the search to some keywords).
This plugin will work out-of-the-box with most themes using the included 404 template.
You can also use this plugin’s functionality in your theme’s 404 template to fine tune the look and feel to match your theme.