URL-Checker is a Java-Application, which periodically connects to a specified URL and writes the results (ie "connection OK/failed") to a logfile. A nice tool for webmasters to monitor the availability of a website. There is a GUI and a non-GUI-edition
Monitoring tool with support to Websites, RSS, Webservices and Databases. Has notifications by email and RSS and you can access metrics like availability, latency and load time by a web-based GUI. Runs standalone with an embedded HTTP server.