Aria2 是一個多平臺輕量級，支持 HTTP、FTP、BitTorrent 等多協議、多來源的命令行下載工具。Aria2 可以從多個來源、多個協議下載資源，最大的程度上利用了你的帶寬。Aria2 有著非常小的資源占用，在關閉磁盤緩存的情況下，物理內存占用通常為 4M（正常 HTTP/FTP 下載的情況下），BitTorrent 下載每秒2.8M/S的情況下，CPU 占有率約為 6%。Aria2 支持 JSON-RPC 和 XML-RPC 接口遠程調用。

很多人在 Windows 可能用過 Internet Download Manager，是很好用的多線程下載工具。Aria2 跟 IDM 類似，不僅可以多線程下載，還可以通過多來源進行下載，簡單的說就是從多個鏡像服務器同時下載一個文件，Aria2 還支持 BT 協議，彌補了 IDM 只支持 HTTP 和 FTP 的痛點。

Linux下的軟件截圖：

Windows 下的軟件截圖

特性：

• Command-line interface
• Download files through HTTP(S)/FTP/SFTP/BitTorrent
• Segmented downloading
• Metalink version 4 (RFC 5854) support(HTTP/FTP/SFTP/BitTorrent)
• Metalink version 3.0 support(HTTP/FTP/SFTP/BitTorrent)
• Metalink/HTTP (RFC 6249) support
• HTTP/1.1 implementation
• HTTP Proxy support
• HTTP BASIC authentication support
• HTTP Proxy authentication support
• Well-known environment variables for proxy:?http_proxy,?https_proxy,?ftp_proxy,?all_proxy?and?no_proxy
• HTTP gzip, deflate content encoding support
• Verify peer using given trusted CA certificate in HTTPS
• Client certificate authentication in HTTPS
• Chunked transfer encoding support
• Load Cookies from file using the Firefox3 format, Chromium/Google Chrome and the Mozilla/Firefox (1.x/2.x)/Netscape format.
• Save Cookies in the Mozilla/Firefox (1.x/2.x)/Netscape format.
• Custom HTTP Header support
• Persistent Connections support
• FTP/SFTP through HTTP Proxy
• Download/Upload speed throttling
• BitTorrent extensions: Fast extension, DHT, PEX, MSE/PSE, Multi-Tracker, UDP tracker
• BitTorrent?WEB-Seeding. aria2 requests chunks more than piece size to reduce the request overhead. It also supports pipelined requests with piece size.
• BitTorrent Local Peer Discovery
• Rename/change the directory structure of BitTorrent downloads completely
• JSON-RPC (over HTTP and WebSocket)/XML-RPC interface
• Run as a daemon process
• Selective download in multi-file torrent/Metalink
• Chunk checksum validation in Metalink
• Can disable segmented downloading in Metalink
• Netrc support
• Configuration file support
• Download URIs found in a text file or stdin and the destination directory and output file name can be specified optionally
• Parameterized URI support
• IPv6 support with Happy Eyeballs
• Disk cache to reduce disk activity