I like Download Booster feature of Samsung Galaxy S5. You can use both Wi-Fi and 4G connections to speed up your file download. Yes, lot of time will be saved. Guess what? There is actually an Android application 2 years ago called Super Download which do the very same thing ~ download web files with Wi-Fi and mobile data at the same time. And it does not limit to 4G only. You can use 3G data connection as well. As usual, root access is required for good stuff.
Note – The lite version has a file size limit of 50 megabytes. Buy the full version if you have large size file to download.
Download Super Download here.
