Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Troops Slack Sales Gong - The most customizable Salesforce Gong in Slack
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Attentive - A marketing channel, built for retail & e‑commerce
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
StatusOk (Open source) - Get notified through Slack/email when your website is down