steelme is a theme manager for Java Swing programs. It allows end users to select from pre-installed themes (color/font schemes) or to create their own themes by using the ThemeEditor. steelme is designed to be lightweight and easy for the application developer to use, and it provides some functionality to export themes as Cascading Stylesheets.
mySkin (formerly SkinDIA!) is an instant DIA skin loader and manager for the Palm Tungsten T3, T5, LifeDrive, and TX. Among many other features, it lets you load T3 skins on the T5, LifeDrive, and TX, insert photos into skins (not on the T3), mix and colorize elements of skins, etc.
IDesk provides icons on an X11 desktop. Its features include transparency, configurable actions to run shell commands, PNG, SVG (in old versions), GIF image support, and XFT anti-aliased fonts. Other features include Imlib2 support (Imlib is deprecated), pseudo-transparency, the ability to only show captions on mouseover, tooltip on mouseover, startup notification, and more.