JDownloader

JD has a design, as far as I know, called "Windows Native". That makes JD looks like a real Windows application.
On Mac OS, you can't do this. Be honest, all styles on Mac are very ugly (you can see an example how JD looks like on Mac OS in the attachment: jd look.png).
In file "native look.png" you can see how a Mac application should be, like Finder does.

Important things:

• the menu with entries like "Datei, Links, Premium, Erweiterungen" should be on the top on the screen (see native look.png)
• the aqua style isn't that bad so we can use it
• red, yellow and green buttons instead of X _ O
• the corners of the windows
• splash screens aren't very common on mac. the dock symbol jumps instead until the program is opened
• and so on

Some links which might help:

• Mac OS X Integration for Java: http://developer.apple.com/mac/library/documentation/Java/Conceptual/Java14Development/07-NativePlatformIntegration/NativePlatformIntegration.html#//apple_ref/doc/uid/TP40001909-SW1
• Apple Human Interface Guidelines: http://developer.apple.com/mac/library/documentation/UserExperience/Conceptual/AppleHIGuidelines/XHIGIntro/XHIGIntro.html#//apple_ref/doc/uid/TP30000894-TP6
• Making Swing Applications look more like native Mac OS X applications: http://www.devdaily.com/apple/mac/java-mac-native-look/

Thank you.