Ping Pong is a MacOS-X application which continuosly checks if specified remote hosts are available and notifies You if they are down (and if they are up again). You can select how often you want "ping" to happen, choose method of notification (visual, voice, email, etc.).
If you need to monitor a busy server which doesn't always respond in time you can specify the number of lost packets which is tolerable.
Full Specifications
What's new in version 1.2.1
General
ReleaseApril 27, 2009
Date AddedApril 25, 2009
Version1.2.1
Operating Systems
Operating SystemsMac OS X 10.4 PPC, Mac OS X 10.5 PPC, Mac OS X 10.4 Intel, Mac OS X 10.5, Mac OS X 10.5 Intel, Macintosh, Mac OS X 10.4