ratpoison binary package in Ubuntu Bionic s390x

 ratpoison is a simple window manager with no fancy graphics,
 no window decorations, and no rodent dependence.
 It is largely modelled after GNU Screen.
 .
 The screen can be split into non-overlapping frames. All
 windows are kept maximized inside their frames to take
 full advantage of your precious screen real estate.
 .
 All interaction with the window manager is done through
 keystrokes. ratpoison has a prefix map to minimize
 key clobbering.

Source package