aria2 is a lightweight multi-protocol & multi-source command-line download utility. It supports HTTP/HTTPS, FTP, SFTP, BitTorrent and Metalink, etc.
License: Open Source
Aria2 is a command-line based downloader known for its lightweight and fast performance, supporting a wide range of protocols and offering extensive customization, but it lacks a GUI. FlashGet, on the other hand, is a user-friendly downloader with a graphical interface, offering features like download acceleration and file management but may consume more resources.