aria2

aria2 is a command‑line utility that downloads files using HTTP(S), FTP, SFTP, BitTorrent and Metalink protocols. It can fetch a single file from multiple sources simultaneously, combining HTTP/FTP/SFTP and BitTorrent streams to maximize bandwidth. When Metalink is used, the program validates chunk checksums during download, and it can also perform segmented downloading and selective retrieval of files within multi‑file torrents or Metalink archives.

The tool is intended for developers and system administrators who need a lightweight, scriptable downloader that works in terminal environments. It supports proxy configuration via standard environment variables, HTTP authentication, gzip/deflate encoding, IPv6 with Happy Eyeballs, and can operate as a daemon with JSON‑RPC or XML‑RPC interfaces for remote control. Additional features include download/upload speed throttling, peer‑to‑peer extensions, and optional encryption or certificate verification for HTTPS and SFTP.

aria2’s distinctive aspects are its ability to merge different protocols for a single download, its extensive Metalink support with checksum validation, and a rich set of command‑line options that allow fine‑grained control over connections, cookies, headers and disk caching without requiring a graphical interface.