App Engine Server Monitor
This is a web server monitor written to run on Google App Engine. It's quite old but it still works and is being actively used by the original author 24/7.
The interface does not use Ajax, there is nothing but a form for adding new domains to monitor, and a list of servers being monitored. Most of the magic happens in checkservers.py which is used by the App Engine cron system to periodically check the stored domains.
The notification method is via email or Prowl, which is a custom push notification API for iOS devices. I typically use email though, as I get iPhone notifications for those anyway.