GTmetrix - GTmetrix is a free tool that analyzes your page's speed performance. Using PageSpeed and YSlow, GTmetrix generates scores for your pages and offers actionable recommendations on how to fix them.

NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.

PageSpeed Insights - PageSpeed is addon for ...

Server Monitoring - A server monitor is a tool that monitors your server and website on close intervals and reports to you if it's inaccessible.

NewRelic - New Relic is a Software Analytics company that makes sense of billions of metrics across millions of apps. We help the people who build modern software understand the stories their data is trying to tell them.

Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.