ActiveXperts Network Monitor

• The ActiceXperts Network Monitor needs your domain server, the domain name, the type and the IP address -- or multiple addresses, if necessary. The network monitor then checks results against these and reports whether the check succeeds or fails based on the expected information output.
  
  

DNS Watcher

• To monitor your DNS with DNS Watcher, you simply input your domain host name and server name, then run the check. The program window will display whether the check succeeded or failed. The program records the results to a log and can be set to autorun at customized intervals.
  
  

Montastic

• Montastic is a web-based monitoring service that offers several plans, one of which is free. The free plan allows you to set three domains to be monitored; it returns an option of up,indicated with a green icon, or down, a red icon. You can set check intervals between every thirty minutes and once a day. Additionally, you can use the RSS feed to display results into a feed aggregator that sends an email if a site is down.