JDownloader is a Java based aplication for Mac. It is free and open-source, and it will help you download files from several different hosting services on the internet, optimizing downloads and letting you manage multiple active transfers from its own interface.
One of the features that has made JDownloader a success is its capacity of easily downloading files from services such as Mega and Rapidshare, automatically and sequentially processing all files you add to the queue, whether you are a premium user or not.
The program could become your main downloads manager, bringing all your standard internet downloads, those from special services, and even special formats such as YouTube videos, into one place. By copying the YouTube videos' URLs into the program you’ll be able to download them locally.
JDownloader is a very interesting application for users who download several files from the internet daily and who want to automate the whole process.