Peter Westwood

This plugin allows your users to configure a reminder to be sent to them if they haven’t posted in the last n days.
You configure the reminder on your Profile page (or the profile of another user if you have than capability)
It is in the Personal Options section and called Blogminder Threshold

PJW Blogminder

This plugin allows your users to configure a reminder to be sent to them if they haven't posted in the last n days.

madebyiman

Smart Renew Tracker helps you stay on top of your clients’ renewals. 
Never lose track of domain, hosting, or SSL expiry dates again — the plugin shows you clear dashboard alerts and sends automated email notifications before your renewals expire.
Perfect for: 
– Freelancers who manage multiple client sites 
– Web agencies with recurring hosting or domain renewals 
– Business owners who want automatic reminders
Main Features: 
– Add and manage renewals (domain, hosting, SSL, etc.) 
– Dashboard alerts for upcoming renewals 
– New: Automated Email Notification system 
– New: AJAX-powered “Send Test Email” for instant verification 
– Customizable alert threshold (number of days before expiry) 
– Clean, minimal design and easy-to-use interface
This plugin runs entirely inside your WordPress dashboard — no third-party APIs or external dependencies.
<h3>License</h3>
This plugin is licensed under the GPLv2 or later.

Smart Renew Tracker

A lightweight plugin to track and manage your domain, hosting, and SSL renewals directly inside WordPress.

PJW Blogminder vs Smart Renew Tracker