Epidermis theme manager is an open source GTK application for managing, automatically downloading and installing themes of various types, in order to transform the look of your Ubuntu desktop.
Dynamic wallpaper is based on weather-wallpaper and generates svg wallpaper based on current weather, season, time of day and others. It supports themes. The intended use is for GNOME desktop and will probably work on KDE.
Icon theme creation software. It is very easy to use. It let you select custom icons for different categories, save them and build icon themes from them. It have a drag 'n drop interface, that makes theme creation very easy. Requires : libglade, python