"aria2 is a lightweight multi-protocol & multi-source command-line download utility. It supports HTTP/HTTPS, FTP, BitTorrent and Metalink. [...] [S]ource distribution and binaries [are available] for OS X, Windows and Android."
"Features
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. When disk cache is off, 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, Local Peer Discovery and UDP tracker.
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."
From http://aria2.sourceforge.net/:
"aria2 is a lightweight multi-protocol & multi-source command-line download utility. It supports HTTP/HTTPS, FTP, BitTorrent and Metalink. [...] [S]ource distribution and binaries [are available] for OS X, Windows and Android."
"Features