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.

Gilbert Pellegrom

Hate when you get those ugly errors and warnings in your WordPress admin area (especially when WP_DEBUG is turned on)? 
WP Admin Error Handler sorts that out by catching all the errors and warnings and displaying them neatly in the admin bar 
so you can read them at your convenience.

WP Admin Error Handler

Taming WordPress and PHP errors and displaying them properly.

404 Site Checker vs WP Admin Error Handler