dsh

dsh (the distributed shell) is a program which executes a single command on multiple remote machines. It can execute this command in parallel (i.e., on any number of machines at a time) or in serial (by specifying parallel execution of the command on 1 node at a time). It was originally designed to work with rsh, but has full support for ssh and with a little tweaking of the top part of the dsh executable, should work with any program that allows remote execution of a command without an interactive login.