aria2c(1) -j5 -i list.txt
The ultra fast download utility
-j, --max-concurrent-downloads=N
    Set maximum number of parallel downloads for every static (HTTP/FTP) URI, torrent and metalink. See
    also -s and -C option. Default: 5
-i, --input-file=FILE
    Downloads URIs found in FILE. You can specify multiple URIs for a single entity: separate URIs on a
    single line using the TAB character. Reads input from stdin when - is specified. Additionally,
    options can be specified after each line of URI. This optional line must start with one or more white
    spaces and have one option per single line. See Input File subsection for details.
source manpages: aria2c