Tmux is an alternative for screen. For anyone who doesn't know screen, it is a terminal multiplexer which means, it allow multiple windows in terminal. It can split your window into multiple panes (vertical/horizontal), detach a session which can be attached at a later time. Detach/Attach is very useful for running a job in a remote server without having to keep the ssh open the whole time.
Tmux can be configured by ~/.tmux.conf file.
My prefix key is Ctrl-q.
If you want to send your keystrokes to all the panes in your tmux window:
<prefix> :setw synchronize-panes
In my case I do:
This is immensely useful if you want to execute the same set of commands on multiple servers.