Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Probe - Revenue metrics. Sales metrics. Business costs. All in one place.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
BareMetrics - SaaS Analytics for Stripe
Better Uptime - We call you when your website goes down
GetMetrics - Metrics and notifications for Stripe - Know what's going on in your Stripe account. Instant event notifications and metrics.