Aria2
"aria2 is a lightweight multi-protocol & multi-source command-line download utility. It supports HTTP/HTTPS, FTP, SFTP, BitTorrent and Metalink. aria2 can be manipulated via built-in JSON-RPC and XML-RPC interfaces." - https://aria2.github.io/
Of particular interest is the ability to download a single file from multiple sources, even using multiple protocols, to have increased download speed.
Examples
Download a file in place
This command can be canceled and given again to resume the file download.
## -x5 Connect once to each server
## -c Continue a partially downloaded file (HTTP/FTP)
## --file-allocation=none Do not pre-allocate disk space for the file (begin downloading immediately. see man page for more options.)
## --max-overall-download-limit=3 (K = 1024, M = 1024K)
## --max-download-limit=1M per connection speed limits
aria2c -x5 -c --file-allocation=none --max-overall-download-limit=3 --max-download-limit=1M http://example.com/foo.iso