Wily monitors the status of DHI servers by asking them for data and making sure the data they return is free of obvious errors. It publishes what it finds through a servlet, and can also be configured to send email if the status of a server changes between subsequent runs.
A version of wily in action can be seen here.
The servlet runs inside of Tomcat and makes a webpage containing the status of all the DHI servers it knows about along with the status of some regular websites to indicate if just basic internet connectivity could be the problem. A link leads from each DHI server to a page with results from a query to that server.
You can see a live wilycat here.
WilyMail is designed to be run periodically (every 30 minutes or so by cron) to check if the status of a server has changed. If it has changed, WilyMail sends an email to interested parties letting them know the current status of the servers.
You can get the latest version of Wily here. Both WilyMail, the servlet, and of their dependencies are in this tar file.