Download manager is a program designed to download files from the Internet, unlike a browser, which is mainly intended to browse pages on the WWW (with file downloading being of secondary importance).
There are several things that browsers are not very good at. That's where the download managers enter the equation.
Download managers are necessary for every heavy Internet user. For dial-up users they can automatically dial the ISP at night, when tariffs are usually lower, download the specified files and hang-up. They can record what links the user clicks on during the day and queue these files for later download. For broadband users, download managers can help download 100+ megabyte files by resuming broken downloads, by limiting download capacity used so that user's browsing is not affected much, or by automatically browsing a site and downloading content specified by user (photo galleries, MP3 collections, etc.), including automatically downloading whole sites and regularly updating them.
Most download managers today integrate seemlessly with popular browsers and are extremely easy to use. Clicking on a link in a browers automatically starts the download in the download manager. For power users additional features are available, such as scheduling, traffic shaping, virus-checking, cataloguing, etc.
Among the most popular download managers are Download Accelerator, ReGet, GoZilla and GetRight. Offline Explorer is the most powerful program for recursive site downloads. For command line users there is wget, in which most of the advanced functionality can be reproduced by using complex command line parameters.
Related to download managers are two other breeds of Internet programs - filesharing peer-to-peer applications (KaZaA, eMule, BitTorrent) and stream recorders (such as StreamBox VCR).