aria2 is a multi-protocol download manager and BitTorrent client. It functions as a command-line utility and a background daemon capable of retrieving files via HTTP, HTTPS, FTP, SFTP, BitTorrent, and Metalink.
The project distinguishes itself by supporting multi-source downloading, which allows a single file to be retrieved from several different sources and protocols simultaneously. It operates as a download server by exposing JSON-RPC and XML-RPC interfaces over HTTP and WebSocket, enabling remote task management from external programs.
The system optimizes throughput by splitting files into segments for parallel downloading and maximizing bandwidth utilization. It includes peer-to-peer capabilities such as Distributed Hash Table peer discovery, UDP tracker integration, and peer exchange.
Data integrity is maintained through cryptographic checksum validation, while network access is managed via session cookies, secure HTTP authentication, and transfer speed throttling.
