If you‘re run an Apple X-Serve, then you won’t need it 'cause of the really good Server Monitor Application which checks all services and the physical elements (fans, temperature, disks etc) of the server. On the otherhand, if not, you may be interested in this little application.

Simple Server Sentry: “Simple Server Sentry is, as described by the name, a simple application that can check on your servers at specified intervals to see if they respond. It was developed for our own in-house use to keep tabs on our own servers, and we thought it was handy enough to share with others.”

It could do with a total GUI overhaul, but it does what it says on the tin.