Integrio Uptime Scout lets you monitor the availability (uptime) of your websites and notifies you if the website/server goes down. It supports different notification methods, such as popup messages, sound alerts and email. Alert notifications can also trigger execution of user defined commands or a third-party application.
[advt]If you are already signed up for commercial web monitoring service, Uptime Scout is still useful – in most cases it notifies you much faster because alert immediately pops up on your screen, and monitoring frequency can be set as low as 30 seconds (most commercial web services offer 5 minute minimum which makes a big difference when the site goes down). It also does not have the delay of email or SMS delivery which in some cases might be critical.