Comment 5 for bug 460778

In the freedesktop specification, there are additional categories for GNOME, KDE, QT, and some others, although there are none for LXDE and XFCE. Maybe these Additional Categories could be included in the freedesktop.org specs, but I think that could be long and hard, and as mentioned on http://blog.lxde.org/?p=361, LXDE and XFCE do not fully comply with the freedesktop.org specification.

After including LXDE and XFCE as additional categories in the freedesktop desktop entry specs, the answer for the last three questions would be to use the Categories from the Desktop entry. Although this still wouldn't eliminate the need for a design for showing applications categorized by toolkit.