NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Platypus - Realtime server monitoring and reporting
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.
OpsDash - All-in-one solution for monitoring servers, services, uptime and databases. Curated Dashboards. Rule-based alerting.
mackerel.io - mackerel.io is a server and application performance monitoring platform.
Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.