While managing server clusters I often want to open SSH session to a dozen of machines and have them run the same set of commands, interactively. So I wrote tmux-sync to do this:
tmux-sync my-session 'ssh host1' 'ssh host2' 'ssh host3' 'ssh host4'
The above command drops you into a tmux session like below. Your input will be sent to all the panes in tmux:
The source code: