Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Site24x7 - Site24x7 offers both free & paid website monitoring services. Monitor websites remotely and receive instant email/sms alerts if your website becomes unavailable. View uptime & performance graphs of your website monitors.
Sumo Logic - Sumo Logic is a secure, purpose-built cloud-based machine data analytics service that leverages big data for real-time IT insights
PagerDuty - Cloud based monitoring service
Pulseway - Pulseway changes the enterprise monitoring and management game with its mobile management solution.
OpsGenie - Alerting and On-Call Management for Dev&Ops Teams