My OSX/Karabiner keyboard layout...

private.xml

<?xml version="1.0"?>
<root>
  <name>My, ehm, stuff.</name>
  <replacementdef>
    <replacementname>WEIRDOAPPS</replacementname>
    <replacementvalue><![CDATA[<only>EMACS, TERMINAL, X11, VIRTUALMACHINE</only>]]></replacementvalue>
  </replacementdef>
  <item>
      <name>Command_R to Option_R (only in Emacs, Terminal, X11)</name>
      <identifier>sitagi.cr_to_or</identifier>
      {{WEIRDOAPPS}}
      <autogen>__KeyToKey__ KeyCode::COMMAND_R, KeyCode::OPTION_R</autogen>
  </item>
    <item>
      <name>Command_L to Option_L (only in Emacs, Terminal, X11)</name>
      <identifier>sitagi.cl_to_ol</identifier>
      {{WEIRDOAPPS}}
      <appendix>(Pass-Through Command+Tab)</appendix>
      {{ COMMAND_L_TO_OPTION_L_EXCEPT_TAB_EXTRA }}
	<include path="/Applications/Karabiner.app/Contents/Resources/include/checkbox/snippets/modifier_tab_to_command_tab.xml">
        <replacementdef>
          <replacementname>FROM_MODIFIER</replacementname>
          <replacementvalue>COMMAND_L</replacementvalue>
        </replacementdef>
        <replacementdef>
          <replacementname>TO_MODIFIER</replacementname>
          <replacementvalue>OPTION_L</replacementvalue>
        </replacementdef>
      </include>
    </item>
  <item>
      <name>Option_R to Command_R (only in Emacs, Terminal, X11)</name>
      <identifier>sitagi.or_to_cr</identifier>
      {{WEIRDOAPPS}}
      <autogen>__KeyToKey__ KeyCode::OPTION_R, KeyCode::COMMAND_R</autogen>
  </item>
  <item>
      <name>Option_L to Command_L (only in Emacs, Terminal, X11)</name>
      <identifier>sitagi.ol_to_cl</identifier>
      {{WEIRDOAPPS}}
      <only>EMACS, TERMINAL, X11</only>
      <autogen>__KeyToKey__ KeyCode::OPTION_L, KeyCode::COMMAND_L</autogen>
  </item>
  <item>
    <name>Return to Control_L</name>
    <appendix>(+ When you type Return only, send Return)</appendix>
    <identifier>sitagi.ret2ctrl</identifier>
    <autogen>__KeyOverlaidModifier__ KeyCode::RETURN, KeyCode::CONTROL_L, KeyCode::RETURN</autogen>
  </item>
</root>