For those who would prefer a graphical interface for their multithreaded downloading, I highly recommend webui-aria2, which (of course) uses aria2c in it's backend: https://github.com/ziahamza/webui-aria2

It's super easy to install locally since it's basically a JS app in a couple of HTML files. For ease of use, I have a shortcut to the index.html in my browser and launch aria2 on startup from my .zshrc.