Simple Server Sentry for Mac

From Lizeric, Inc.:

Simple Server Sentry is exactly what the name implies: a simple application that will check on your servers (web, email, ftp, 4D, etc) to make sure that they are still running. You can either do a simple "ping" to make sure the machine is still alive, or you can actually log into many server types to insure that they are responding as you would expect. If there's a problem, SSS will send you email (including to a cell phone if your carrier supports email-to-text messages) letting you know there was a problem.

You can use the program for free to monitor a single server, or purchase a Personal license to monitor up to 5 servers, or a Pro license to monitor up to 25 servers.

Don't be the last to know when your servers are down!