Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Recurrr - Send recurring emails
Better Uptime - We call you when your website goes down
FollowUpThen - The simplest way to schedule an email reminder