JDownloader is a Download Manager written in Java. JDownloader can download normal files, but also files from online file hosting services like Rapidshare.com.
For running JDownloader you need Java installed. I recommend OpenJDK, it works flawless on Arch Linux.
# pacman -S openjdk
JDownloader can be downloaded from the official website JDownloader.org. On the navigation bar choose Download and then pick a Mirror for the Linux binary distribution. After unpacking the ZIP file, you can move the directory anywhere you want, a good destination might be ~/JDownloader/.
Adding a Menu item
Edit your menu and use the following command to start JDownloader:
java -jar /path/to/JDownloader.jar
To run JDownloader cd to the JDownloader directory and run
$ java -jar JDownloader.jar
Or click on your created menu item.
When you first start JDownloader you can choose your preferred language and also your download directory. On the next window, JDownloader asks you if you want to install FlashGot, a Firefox extension. I recommend clicking on Cancel. If you want this extension, you can still download it through the official mozilla addons website.
Tips and tricks
Making JDownloader faster
In its default configuration, JDownloader is very slow and uses a lot of resources. You can atleast make it a bit faster by applying the following changes in the Settings Tab.
Choose General and then turn the logging level to OFF.
Choose User Interface and then switch the style to Light(GTK). (If you're using GNOME).