ThemeShock

Custom 404, helps you customize your 404. 
From the dashboard options you’re able to modify the background, the image and the fonts color and style.
This page will show users the last post on your site, so that they may choose to follow one of this instead of leaving your page.
<h3>Features</h3>
<ul>
<li>Customizable background</li>
<li>Several Patterns</li>
<li>Multiple fonts</li>
<li>24 additional images.</li>
<li>5 Different languages</li>
</ul>

Custom 404 Error Page: Unilimited designs and colors

Custom 404, creates a 404 page that is set to the default one of your WordPress installation.
This page is fully customizable from the dashboard.

loopj

Automatically detects errors & crashes on your WordPress site using BugSnag to notify you by email, chat or issues system.
All websites crash from time to time, including WordPress sites! Th BugSnag Error Reporting plugin automatically detects crashes, exceptions and other errors in your WordPress PHP code as well as any errors in plugins you are using.
Errors are sent to your <a href="https://bugsnag.com" rel="nofollow ugc">BugSnag Dashboard</a> for you to view and debug, and we’ll also notify you by email, chat, sms or create a ticket in your issue tracking system if you use one. We’ll also show you exactly how many times each error occurred, and how many users were impacted by each crash.

BugSnag Error Monitoring plugin

The plugin is easy to set up; all errors can be monitored via the Bugsnag dashboard. You can also set different log levels and differ between the environments (dev/production) of your website.

Bonus: There are lots of cool integrations like Slack (Push Notifications), GitHub (New Issues) and much more!

Easy error monitoring

Seamless integration with Bugsnag, just perfect.

Works great, people are just dumb

This plugin used to be one of the best tools out there, however, it seems like is not being maintained anymore. 

There is no support for the recent releases of PHP (8.0, 8.1). Recent support requests are not being handled anymore as well.



Abandoned.

Automatically detects errors & crashes on your WordPress site using BugSnag to notify you by email, chat or issues system.

Custom 404 Error Page: Unilimited designs and colors vs BugSnag Error Monitoring plugin