There are plenty of them available.
Steadyflow
Steadyflow is a simple and easy to use download manager, written in GTK. It has a lot of good features without any unnecessary complexity.

It also has an indicator applet.

Install: sudo apt-get install steadyflow
Uget
uGet is a multi-platform GTK3 download manager that supports resuming downloads, comes with categories support, can download torrent and metalink files through aria2, a powerful command line download tool that's integrated into uGet.

Install:
sudo add-apt-repository ppa:plushuang-tw/uget-stable
sudo apt-get update
sudo apt-get install uget aria2
Jdownloader
JDownloader is a free and open source cross platform (Linux,Mac ..) download manager, written in Java, which allows the automatic download of files and split files from one-click. Additionally, many “link encryption” sites are supported – so you just paste the “encrypted” links and JD does the rest.
Install:
sudo add-apt-repository ppa:jd-team/jdownloader
sudo apt-get update
sudo apt-get install jdownloader-installer
Aria
Aria is not a GUI download manager, but it can be used via several Firefox extensions. Two of them are:
Install: sudo apt-get install aria2
Gwget
Gwget is a gnome frontend for the popular downloading application wget. gwget also has firefox integration with the help of the firefox extension FireGet. However, it is not updated since 2009.

More Information
Steadyflow
Uget
Jdownloader
sudo add-apt-repository ppa:tahutek-team/prozilla
,sudo apt-get update
,sudo apt-get install prozilla
.