UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
Troops Slack Sales Gong - The most customizable Salesforce Gong in Slack
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Attentive - A marketing channel, built for retail & e‑commerce
Robodash - Cron and uptime monitoring dashboard
StatusOk (Open source) - Get notified through Slack/email when your website is down