libtorrent (also known as libtorrent-rasterbar) is an open source, efficient, completely free and easy-to-use software implemented in C++ and designed from the offset to act as a very good alternative to all existing BitTorrent implementations.
Not a BitTorrent client per se
Even if it includes a working client, for example purposes only, keep in mind that libtorrent is a library software and not a full featured BitTorrent client. Its main goals are to be CPU efficient, memory efficient, and very easy to use.
In other words, application developers can use libtorrent to add BitTorrent functionality to their projects, no matter if they are dedicated BitTorrent clients or just software that support downloading of torrent files.
Supports the uTorrent transport protocol
libtorrent has been engineered in such a way that it supports a wide range of protocols, including the uTorrent transport protocol, DHT (Distributed Hash Table), UDP (User Datagram Protocol) tracker protocol, Peer extension protocol, as well as the IPv6 tracker protocol.
Among other features, we can mention support for private torrents, superseeding support, HTTP seeding (hoffman-style) support, support for multiple trackers, webseed (GetRight-style) support, tracker returning external IP, and support for magnet links.
Offers a cross-platform BitTorrent implementation
libtorrent is a cross-platform software that has been successfully compiled, installed and tested on numerous operating systems, including GNU/Linux, Microsoft Windows, Mac OS X, SunOS, and Cygwin. It runs on computers supporting either of the 32 or 64-bit CPU architectures.
It can be easily installed on all Linux kernel-based operating system by compiling the source package, which is distributed for free on Softpedia or the project’s homepage (see link below). Simply download the source package and save it on your Home directory. Unpack it using an archive manager tool, open a Terminal app and navigate to the location of the extracted archive files (e.g. cd /home/softpedia/libtorrent-rasterbar-1.0.3), run the ‘./configure && make’ command to configure and compile the software, followed by the ‘sudo make install’ command to install it.