Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.
ServerSuit - ServerSuit is a browser based program that enables remote Linux administration, monitoring, website hosting, and server setup automation.
DownDetector - A simple service to tell you whether a website is down.
AppZero - AppZero is a monitoring and migration tool that allows users to keep track of different applications and servers in both simple and complex IT environments.
Pingbreak - Pingbreak is an original and free monitoring service.
CULA - A webmonitoring solution for beginners and pros.