Platypus - Realtime server monitoring and reporting
OpsDash - All-in-one solution for monitoring servers, services, uptime and databases. Curated Dashboards. Rule-based alerting.
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Healthy Servers - Making server monitoring easy
Web Uptime - Multi-location website uptime monitoring
Dhound - Simple security monitoring for web servers, clouds and apps.