aria2 is a utility for downloading files. The supported protocols are HTTP, FTP, BitTorrent (DHT, PEX, MSE/PE), and Metalink.
It can download one or more files individually or from multiple sources/protocols at the same time and tries to utilize your maximum download bandwidth (by using multiple threads and downloading data from HTTP/FTP, while also uploading to the BitTorrent swarm).
Using Metalink's chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.
The physical memory usage is typically 3MB(normal HTTP/FTP downloads) to 6MB(BitTorrent downloads). CPU usage in BitTorrent with download speed of 1500KB/sec is around 6%.