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.

vmihailenco

airbrake

benarent

This plugin collects and aggregates all errors created by WordPress and it’s plugins. It de-dupes and lets developers know how to fix issues fast.

Airbrake

License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html

Airbrake is collects all errors created by Wordpress and it's plug …

404 Site Checker vs Airbrake