Jaap has asked for the wisdom of the Perl Monks concerning the following question:

I am currently maintaining a webserver for a (long-term) project at school. It would be nice to have some sort of alarmbell going off if the thing stops working.

I could make something myself, but it would have to run on a 2nd server somewhere offsite for best results.

I can imagine more sysadmins would be in the same situation. Does anyone know of a free server monitoring tool/site/something? How would you monitor the server? Any thoughts?