why- Open BSD .rocks

tmux(1) (∞)

tmux, created by Nicholas Marriott, is an in-base, BSD licensed terminal multiplexer. It enables a number of terminals to be created, accessed, and controlled from a single screen. tmux may be detached from a screen and continue running in the background, then later reattached.

There is also a portable version of tmux for non-OpenBSD machines.