Observu - Observu offers website, server and API monitoring solutions.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.
Pingspace - Pingspace is a cost-effective website uptime monitor for your websites, it checks your site uptime...
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Uptrends - Uptrends is a website and mobile app that allows you to monitor your website. You can use it to both monitor the security and performance of your website as well as the activity on your site. Read more about Uptrends.