NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.

Netumo - Ensure healthy website performance, uptime, and free from vulnerabilities. Automatic checks for SSL Certificates, domains and monitor issues with your websites all from one console and get instant notifications on any issues.

Server Monitoring - A server monitor is a tool that monitors your server and website on close intervals and reports to you if it's inaccessible.

AppZero - AppZero is a monitoring and migration tool that allows users to keep track of different applications and servers in both simple and complex IT environments.

Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.

RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems