George Stephanis

Simple 404 Keyword Insertion creates a page called “404-page” on activation. When a visitor hits a 404, the plugin serves that page with a <code>[404-keywords]</code> shortcode replaced by the sanitized keywords from the request URI. This helps create SEO-friendly 404 pages that reflect the content the visitor was looking for.

Simple 404 Keyword Insertion

Builds a custom 404 page based on the request URL, inserting the keywords from the failed request into your 404-page content.

Steve

This plugin uses custom fields to allow the page title tag to be customised and differ from the actual page title.
Both meta descriptions and keywords can also be added if required.
Page meta details can be modified on any publicly accessible post type, such as posts and pages, as well as custom post types.
Theme and plugin developers should note that it is possible override the page title within your templates by setting <code>$wppm_title = 'Newly defined title';</code> before the call to <code>get_header();</code>.

Page Meta

Adds the ability to override the page meta title and add in meta descriptions and keywords for pages.

Simple 404 Keyword Insertion vs Page Meta