Free Rapid Downloader (FRD) although still Java-based is a lot lighter than JD and can be used in Ubuntu.
It does not need installation, just execute the frd.sh file.
Make it executable first - changing permissions in properties or fire in terminal
sudo chmod a+x path-of-frd.sh. (copy
frd.sh file and paste in place of
path-of-frd.sh in this line)
If there's an error message that keeps popping-up, ignore it's of no consequence.
From my experience Tucan it's by no means a good alternative (it never worked for me).
There is also ochDownloader (non-java, therefore very light) that I used in Windows and has a Linux version (but it needs compiling I guess, above my capacities).