You can send commands to a running tmux session, eg. http://superuser.com/questions/492266/run-or-send-a-command-to-a-tmux-pane-in-a-running-tmux-session http:/

You can send commands to a running tmux session, eg. http://superuser.com/questions/492266/run-or-send-a-command-to-a-tmux-pane-in-a-running-tmux-session http://superuser.com/questions/492266/run-or-send-a-command-... How far you take it depends on what you'd want out of such a tool. Simple "New Shell", "Close Shell" buttons would be easy; overlaying draggable partitions would be more effort, and less elegant, but still do-able.