UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
Robodash - Cron and uptime monitoring dashboard
Troops Slack Sales Gong - The most customizable Salesforce Gong in Slack
Apex Ping - Uptime & performance monitoring for websites and APIs.