I highly recommend installing WP Crontrol on your WordPress site, but why, you ask? Because, if you’re a Linux admin, you probably love crontab (I do anyway) and if you’re not a Linux admin (I’m sorry … hope that you become one soon!). This plugin allows you to see the equivalent of of crontab on your WordPress install. I’ve found it very helpful in my myriad of WordPress troubleshooting adventures.
Slack Notifications by dorzki
I found Slack Notifications by dorzki a few weeks ago and have really liked it. I setup a bunch of alerts that go to a dedicated Slack channel. One of those alerts is setup to send a slack when an administrator logs into my site, or tries to and fails (tisk tisk tisk). One day I got a few of those failure alerts in Slack and was immediately able to login and make sure everything was okay.