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.

tamlyn

As a theme developer, you want to have WP_DEBUG enabled but you’re not interested in the deprecated warnings created by other plugins. Use this plugin to disable these messages while still displaying other errors, warnings and notices.
<a href="http://outlandishideas.co.uk/blog/2012/06/hide-deprecated-errors-in-wordpress/" rel="nofollow ugc">Plugin by Outlandish Ideas</a>

Disable Deprecated Warnings

Prevents plugins from showing deprecated errors in the WordPress admin.

404 Site Checker vs Disable Deprecated Warnings