How can I theme my Qt app to resemble one written in Gtk?

Note: this is useful to desktop users, not to developers using Qt.

sudo apt-get install qt4-qtconfig, then go to System / Preferences / Qt 4 settings and select GTK style in the first combobox:

Qt apps don't follow the font hinting settings that are set by gnome-appearance-properties. You need to explicitly add an entry to $HOME/.fonts.conf e.g.

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
 <match target="font" >
  <edit mode="assign" name="rgba" >
   <const>rgb</const>
  </edit>
 </match>
 <match target="font" >
  <edit mode="assign" name="hinting" >
   <bool>true</bool>
  </edit>
 </match>
 <match target="font" >
  <edit mode="assign" name="hintstyle" >
   <const>hintfull</const>
  </edit>
 </match>
</fontconfig>

From nagul's SU post https://superuser.com/questions/37444/how-can-i-make-kde-and-other-non-gnome-apps-inherit-the-ubuntu-theme - direct quote:

Check QGtkStyle, a project to create a GTK+ layer for Qt-based applications (like KDE) running on GTK2-based desktops (like Gnome).

There are other ideas and scripts in the discussion on this topic at Ubuntu Brainstorm: Idea #1744: GNOME themes should affect Qt themes, and more of them in this discussion Idea #1714: GNOME QT integration (and the numerous duplicate ideas gathered under this question).

One of the noteworthy attempts is UniformUI, which attempts to automate configuration of Qt settings to match the current Gtk+ style, partially using QtCurve and QGtkStyle to achieve this.

Fourth google result for "skin qt to match gtk"