Ambit uses Bash brace expansion to expand and list hostnames or commands. Ambit is first and foremost meant to be a general purpose hostlist enumerator for use by other applications or scripts. Ambit can be used to manage HostGroups from the context of a user, a system, or a network. Ambit is also able to enumerate and execute commands that contain expandable elements. Commands passed to Ambit are expanded into separate statements and executed synchronously. This means Ambit can expand and execute just about anything on the command-line and often works in situations where Bash brace expansion would probably fail.
Massh makes it possible to run remote commands, push/execute scripts, and push/pull files on hundreds or even thousands of hosts in parallel. Massh uses Ambit or a similar host list generator to enumerate a list of targets for which it will execute one of the aforementioned operations. Hosts can be logically grouped and dynamically managed, allowing for consistent operational state and improved overall manageability.
I just submitted a new release. You can get it at http://m.a.tt/er/massh.html