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.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
Better Uptime - We call you when your website goes down
Mail Backup X - Your one stop mail backup and archiving tool for Mac.