You may be in doubt that whether Internet Download Manager is the most popular download manager or not? well, its one best the best downloader, It is also called IDM , It is a shareware download manager , It is available only for the Microsoft Windows OS. It provides you the facilities/ options to save,resume,schedule anytime.
Internet Download Manager (IDM) plugin will be auto installed and integrated to the browser either it may be chrome or firefox when you install it , These plugins will help to popup the download now window/option whenever it find any media file playing in the loaded web page. So,you can download even YouTube videos while watching them without installing any YouTube downloader.