jDownloader Portable is the portable version of this popular download manager.
With jDownloader Portable you will be able to download from more than one hundred different sites, which are currently supported but are gradually adding new sites.
To do this, simply insert the USB stick where you have saved the program and you can use it from any computer.
Its interface is simple to use and you won't have any trouble understanding its use.
This program is free and facilitates downloads by controlling the line to improve speed and reduce download time.
If you have any doubts about how it works, this program has a good online help page.