Rapget is a sweat little freeware program that can be used to download multiple files at once from over 60 file hosts including Rapidshare.com, Megaupload, Yourfilehost.com and others. The real beauty of Rapget lies in the fact that it automatically bypasses the annoying captcha that is used on most websites to prevent access with or delay download managers.
It is furthermore possible to add usernames and passwords of select websites to take advantage of memberships and premium accounts. For some services, this is mandatory as the program won't work otherwise at all. I was not able to download files from rapidshare.com for instance without adding premium account details.
Rapget provides a great and easy way to queue as many downloads as you want that are hosted on file hosting websites and download them with the same functionality that a download manager offers. It is furthermore possible to add proxies to Rapget which means that you can bypass country or IP limits that several websites impose upon their users.
Update: Note that Rapget has not been updated since 2008. It is likely that the majority of download options do not work anymore. I suggest you check out the following two alternatives instead.
JDownloader is probably the most popular tool to download files from file hosting sites. It supports hundreds of sites that you can download files from and all the features that you would expect a program of its kind. You can add premium account details to the application to make use of those accounts when downloading files. The open source program supports a variety of features, including options to unpack files automatically - using a password list if necessary -, support for multiple languages, automatic software updates and simultaneous downloads. The only drawback in my opinion is that it requires Java to run.
MiPony is an alternative to that that does not require Java. It is not as comfortable as JDownloader but comes close enough to be a viable alternative. It supports more or less the same sites as JDownloader so pick it up if you do not want to run Java on your system.
Ghacks is a technology news blog that was founded in 2005 by Martin Brinkmann. It has since then become one of the most popular tech news sites on the Internet with five authors and regular contributions from freelance writers.