Well, the perfect downloader that you were looking for is JDownloader. It is open-source, can download from multiple links from a file into a single folder automatically and intercept browser downloads (with an extension). I've never used a premium file sharing host, but JDownloader does have options to log in to your account on many hosts, so that if you have a premium account on one of them, you can get the higher download speeds or bypass any bandwidth limits by the host, etc... I'm not sure about downloading YouTube videos though, I don't think JDownloader has a built in way to download YouTube videos (correct me if I'm wrong).
Piracy
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It does. If you paste a YouTube link, it asks to install FFMpeg, and downloads the video. You can also download audio.
Oh that's nice, I didn't know that
This in combination of free download manager to get download links has help me download large video files from cloud link/browser download
JDownloader is partially closed-source.
Didn't know about that, what parts of it are closed source?
Various plugins, see https://board.jdownloader.org/showthread.php?p=517795
However, it is possible to use JDownloader without these.
Motrix. You can even get an extension for your browser to automatically add downloads to Motrix.
I have tried a lot and always go back to Jdownloader. Nothing really compares IMO
Free Download Manager (FMD). FOSS
Xdman. It is opensource and can download directly from firefox/chrome
Gabut DM check it out.