Pingmon!

Pingmon is written in Perl and is designed to monitor machines on a network to make sure they are live. It is a console based program with a colour interface (can be switched to black & white) which means it can easily be used from a remote machine. You can configure which hosts to monitor, which hosts to ignore and which hosts cause a log entry if they go down. An optional audible alert can be given if a host goes down. Scan speeds can be completely configured to control network traffic. It also supports the use of ICMP (ping request), TCP (echo port) and UDP (echo port) monitoring. It's been tested on Linux, Solaris and IRIX but likely works under any OS with a reasonable perl implementation and a terminal supporting ANSI.