Monitornator - Server monitoring made simple
PagerDuty - Cloud based monitoring service
OpsDash - All-in-one solution for monitoring servers, services, uptime and databases. Curated Dashboards. Rule-based alerting.
VictorOps - We make on-call suck less & help teams to solve problems faster.
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
xMatters - xMatters transforms event data into intelligent communication IT teams, avoiding outages and disruptions