tmux is a "terminal multiplexer". It allows a number of terminals (or windows) to be accessed and controlled from a single terminal. It is intended to be a simple, modern, BSD-licensed alternative to programs such as GNU screen.
License: BSD License (revised)
Changes:
A basic configuration file. New commands: send-keys and show-options. Window options, including maximum width and height. Per-session options (inherited from the global options if not set). The ability to highlight window activity in the status line. Completely reworked, more consistent command argument syntax. Several bugfixes.
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