After Ubuntu and GNOME, KDE will get its own font too: Oxygen.
Oxygen font family is already available for testing (currently in alpha!) and comes with regular, bold and monospace variants, however, only the basic character shapes are done for now and the font is currently using the basic 'auto spacing' from FontForge.
Oxygen Appmenu is an Oxygen style for Kwin that displays the application menu as a button in the titlebar and works with Qt and GTK applications as well as Firefox or Thunderbird:
The menu comes with different styles: 'menu' (first screenshot in the post), an icon or the application name:




