aria2 is a lightweight multi-protocol & multi-source command-line download
utility. It supports HTTP/HTTPS, FTP, BitTorrent and Metalink. aria2 can be
manipulated via built-in JSON-RPC and XML-RPC interfaces. Its features include:
- Multi-Connection Download.
  aria2 can download a file from multiple sources/protocols and tries to utilize
  your maximum download bandwidth. Really speeds up your download experience.
- Lightweight.
  aria2 doesn't require much memory and CPU time. The physical memory usage is
  typically 4MiB (normal HTTP/FTP downloads) to 9MiB (BitTorrent downloads). CPU
  usage in BitTorrent with download speed of 2.8MiB/sec is around 6%.
- Fully Featured BitTorrent Client.
  All features you want in BitTorrent client are available: DHT, PEX,
  Encryption, Magnet URI, Web-Seeding, Selective Downloads and Local Peer
  Discovery.
- Metalink Enabled.
  aria2 supports The Metalink Download Description Format (aka Metalink v4),
  Metalink version 3 and Metalink/HTTP. Metalink offers the file verification,
  HTTP/FTP/BitTorrent integration and the various configurations for language,
  location, OS, etc.
- Remote Control.
  aria2 supports RPC interface to control the aria2 process. The supported
  interfaces are JSON-RPC (over HTTP and WebSocket) and XML-RPC.

WWW: http://aria2.sourceforge.net/