The free Pingdom Desktop Notifier software runs in the background and notifies you if your website is down. It uses the free Pingdom uptime monitoring service and lets you easily get started right inside the application.
The Pingdom uptime monitoring service uses a global network of servers to test your websites uptime and response time, making sure it is working ok. Monitoring one website is totally free. If you want to monitor more than one there are paid options available.
Since the Pingdom Desktop Notifier uses Pingdoms popular monitoring service - already used by tens of thousands of people and companies - you get a ton of bonus features online:
- Full access to all functionality via an online control panel.
- Monitors the uptime and response time of websites, email servers, DNS servers or any type of general service connected to the Internet.
- Downtime alerts via email, SMS, Twitter and iPhone push notifications.
- Charts and statistics for uptime, downtime and response time.
- Error analysis performed automatically to help identify problems.
- Daily/weekly/monthly status reports via email.
- Publicly hosted uptime reports (if you want them).

The license of this software is Freeware, you can free download and free use this server monitoring software.