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.
Firezone - Firezone is a remote access platform that’s painless to deploy, easy to manage, and built on WireGuard® to be blazing fast. Best of all it's self-hosted and open-source.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Viscosity - Viscosity is a VPN client for Mac OS X and Windows.
Better Uptime - We call you when your website goes down
Tunnelblick - free software for OpenVPN on OS X and macOS