What are some alternatives?
When comparing NIXStats and UptimeRobot, you can also consider the following products
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.
StatusCake - StatusCake | Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
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.
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.
RapidSpike - RapidSpike is an uptime and performance monitoring service for websites and web applications.
PHP Server Monitor - PHP Server Monitor is a script that checks whether your websites and servers are up and running.