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.
EasyHook - The reinvention of Windows API Hooking
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Deviare API Hook - Deviare is a professional open source hooking engine for instrumenting arbitrary Win32 functions, COM objects, and functions which symbols are located in program databases (PDBs).
Better Uptime - We call you when your website goes down
madCodeHook - "madCodeHook" offers everything you need to hook code (mostly APIs).