aria2 is a utility for downloading files. The supported protocols are HTTP(S), FTP, BitTorrent, and Metalink. It has a powerful segmented downloading ability, downloading a file from multiple sources and multiple protocols and utilizing your download bandwidth to the maximum. It supports downloading a file from HTTP(S)/FTP and BitTorrent at the same time, while the data downloaded from HTTP(S)/FTP is uploaded to the BitTorrent swarm. Using Metalink's chunk checksums, aria2 automatically validates chunks of data while downloading a file like BitTorrent.
SALI (Sara Automatic Linux Installer) is a tool that allows you to install Linux on multiple machines at once. It support several protocols for downloading by way of aria2 to install a machine. For example, BitTorrent and rsync are supported. SALI originates from SystemImager and still uses the same philosophy. It is a scalable method for performing unattended installation. SALI is mostly used in cluster setups.
KTorrent is a BitTorrent application that allows you to download and share files using the BitTorrent protocol. Key features include queuing of torrents, global and per-torrent speed limits, previewing of certain file types, importing of partially or fully downloaded files, file prioritization for multi-file torrents, selective downloading for multi-file torrents, kick/ban peers with an additional IP Filter dialog for list/edit purposes, UDP tracker support, support for private trackers and torrents, support for µTorrent's peer exchange, support for protocol encryption (compatible with Azureus), support for creating tracker-less torrents, support for distributed hash tables (DHT), support for UPnP to automatically forward ports on a LAN with dynamic assigned hosts, support for webseeds, scripting support via Kross, and interprocess control via DBus interface.
PeerProject is a versatile peer-to-peer filesharing client and file manager. It's intuitive and aesthetic while supporting many networks and features, including BitTorrent, G2, Gnutella, eDonkey, DC++, IRC, HTTP/FTP, and more. It's a mainstream fork of Shareaza p2p, for Windows and WINE.