title: is GTK 3.x a real cross-platform solution?
body: <p>I have tasted both Qt 4.x/5.x and GTKmm 3.x and I really like GTKmm over Qt.</p>
  
  <p>Now I have just discovered that GTKmm 3.x doesn't offer a Windows porting, they also do not offer a Mac porting, basically I can't find nothing but libraries/sources/binaries for Linux.
  Apparently the Windows support ( I'm not sure about the situation for the Mac OS stuff ) was dropped in the 2.x era and it's still not-existing today.</p>
  
  <p>I have planned to use GTK 3.x for specific reasons, especially for some new features introduced by the 3.x branch, so using GTK 2.x is an option off the table.</p>
  
  <p>Now I ask: there is something new for the Windows and/or Mac support for GTK 3.x ? There is something ? even experimental projects ?</p>