For Java there are some good skins ( Look & Feel - LaF ).
On Habré there was an article with a list of LaF-styles for Java , I personally liked Tiny LaF from there, which changes the style of the program in just a couple of lines (of course, after downloading the small library and throwing it into the project):
try { UIManager.setLookAndFeel("de.muntjak.tinylookandfeel.TinyLookAndFeel"); } catch(Exception ex) { ex.printStackTrace(); }
Tutorial with Oracle .
There are also styles for JavaFX , for example, here are native styles.
Modena is also popular:

There is also a style under Mac OS X: AquaFX , but it is strongly recommended to use under Mac OS, because some chips only work on Mac OS:
