As a popular IDE for Java application, Intellij IDEA's look and feel is very beautiful in my opinion.
How did it do that? And how can I get a look and feel like Intellij IDEA in my Swing app?
As far as the Darcula theme goes,
"I'm working on making Darcula a stand alone LaF. The work is almost done and I'm ready to release Darcula v 1.0 alpha or something. This means that you will be able to run you apps like this:
$ java -cp "darcula.jar:myapplication.jar" -Dswing.laf=Darcula MainClass
And everything should work
I'll do an announce when Darcula is ready for publishing"
Konstantin Bulenkov - June 12, 2013
https://plus.google.com/+jetbrains/posts/NNCSHsjGNXD
I couldn't find any recent follow up info though.