xlax is an X11 input multiplexer: keyboard input can be set from a xlax
instance to a group of windows simultaneously. The tool is designed for
system administrators who typically have to do the same thing on several
machines (or in several different directories).
Windows can be added or deleted interactively, or temporarily
disconnected and reconnected.
xlax allows the user to assign a custom string to each window (e.g. a
hostname) that can be sent with a button click.
An included script handles starting up and arranging windows, and
permits to define commonly used window groupings in a config file.

Homepage:
https://hea-www.harvard.edu/~fine/Tech/xlax.html
