The GTK-Qt Theme Engine allows GTK to utilize Qt widget styles.
The way it works is that the GTK-Qt Theme Engine acts just like a normal GTK theme engine, but instead of doing the drawing itself, it calls functions from Qt. This means you get the best of both worlds: the power of GTK and the professional-looking widget styles of Qt.
There are some limitations, however. One issue is an incompatibility between Qt and the GNOME window manager. This means that some parts of GNOME will not be themed by Qt. That said, the theme will still run fine under GNOME - you just won't get a uniform look across the board.
Another problem is that the logout box and window border menus may appear blank when using the theme. This issue can only be resolved by patching Qt itself, which may not be feasible for the average user.
Despite these limitations, the GTK-Qt Theme Engine is definitely worth considering if you're looking to make your cross-platform software look great. It's easy to use and offers a lot of flexibility, making it a must-have addition to your developer toolkit.
Version 1.1: N/A