Ratpoison

/usr/share/xsessions/ratpoison.desktop

[Desktop Entry]
  Name=Ratpoison
  Comment=This session logs you into Ratpoison
  Exec=/usr/bin/ratpoison
  TryExec=/usr/bin/ratpoison
  Icon=
  Type=Application
  X-Ubuntu-Gettext-Domain=ratpoison-session

~/.xmodmaprc

remove Lock = Caps_Lock
remove Control = Control_L
keysym Control_L = Caps_Lock
keysym Caps_Lock = Control_L
add Lock = Caps_Lock
add Control = Control_L