Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Platypus - Realtime server monitoring and reporting
Healthy Servers - Making server monitoring easy
Monitornator - Server monitoring made simple
PING - PING (Partimage Is Not Ghost) is a free software Linux-based live CD ISO built upon the partimage...
OpsDash - All-in-one solution for monitoring servers, services, uptime and databases. Curated Dashboards. Rule-based alerting.