Tmux is a terminal multiplexer, allowing one to track multiple groups of terminals and terminal environments in a Terminal UI application.
It's most often used as a window manager on Unix-based systems without a GUI in conjunction with programs like Vim.
Unfortunately, the tmux configuration language is very limited, but it provides the right facilities for keymapping and managing windows.
https://github.com/tmux-plugins/tmux-pain-control A tmux plugin that offers pane control and standard pane navigation bindings.
Byobu claims to be a more fully-featured window manager built on top of tmux that might be more viable as a day to day interface without an X session. https://zserge.com/posts/tmux/ tmux for mortals