JDownloader is open source, platform independent and written completely in Java. It simplifies downloading files from One-Click-Hosters like Rapidshare.com or Megaupload.com - not only for users with a premium account but also for users who don´t pay. It offers downloading in multiple paralell streams, captcha recognition, automatical file extraction and much more. Of course,
JDownloader is absolutely free of charge. Additionally, many “link encryption” sites are supported - so you just paste the “encrypted” links and JD does the rest. JDownloader can import CCF, RSDF and the new DLC files.

Features:

Platform independent. (Windows, Linux, Mac, ..)
Runs on Java 1.5 or higher
Complete Open-Source (GPL)
24-hour support
Download several files parellel
Download with multiple connections
JD has an own powerful OCR module (JAntiCaptcha)
Decrypt RSDF, CCF and DLC Containerfiles
Decryptplugins for many services. e.g. sj.org, UCMS, WordPress, RLSLog….
Youtube, Vimeo, clipfish video and Mp3 Download
Automatic extractor (including password list search) (Rar archives)
Theme Support
Multilingual
About 75 hoster and over 300 decrypt plug-ins
Reconnect with JDLiveHeaderScripts: (1400 router supported)
Webupdate
Integrated package manager for additional modules (eg. Webinterface, Shutdown)