JDownloader 2
An advanced download manager, JDownloader 2 is optimized for power users
JDownloader 2 is a free, open source download manager with a massive developer community, and it's available for Windows, Linux and Mac.
It's really one for power users, with support for over 300 decryption plugins, automatic RAR extraction, password list searching and OCR to complete some of the CAPTCHA 'I'm not a robot' checks you encounter on download sites.
You'll need the Java Runtime Environment to run it, and you'll need to be careful when installing it: the installer contains adware, which will be bundled in with the download manager if you don't specifically deselect it.
