tmux is the go-to terminal multiplexer for developers and sysadmins who live in the command line. It lets you split a single terminal into multiple panes and windows, switch between them instantly, and—most importantly—detach from a session and reattach later from anywhere. That last feature is gold over SSH: start a long build on a remote server, close your laptop, and pick up exactly where you left off.

Its popularity comes from being lightweight, scriptable, and endlessly configurable through ~/.tmux.conf. Key features include persistent sessions that survive disconnects, flexible pane/window splitting, and a copy-mode for scrolling and selecting text with the keyboard. It also supports shared sessions, making it handy for pair programming.

bash
tmux new -s work      # start a named session
# Ctrl-b %            split vertically, Ctrl-b "  split horizontally
# Ctrl-b d            detach
tmux attach -t work   # reattach later

Once it's in your muscle memory, working without it feels broken.