title: How to add custom item to system menu in C++?
body: <p>I need to enumerate all running applications. In particular, all top windows. And for every window I need to add my custom item to the system menu of that window.</p>
  
  <p>How can I accomplish that in C++?</p>
  
  <p><strong>Update.</strong></p>
  
  <p>I would be more than happy to have a solution for Windows, MacOS, and Ubuntu (though, I'm not sure if MacOS and Ubuntu have such thing as 'system menu').</p>