Azureus (now Vuze) is a java bittorrent client. It provides a bittorrent protocol implementation using java language.
Azureus offers multiple torrent downloads, queuing/priority systems (on torrents and files), start/stop seeding options and instant access to numerous pieces of information about your torrents. Azureus now features an embedded tracker easily set up and ready to use.

Vuze Homepage     Download Vuze

BitComet is a powerful, clean, fast, and easy-to-use bittorrent client. It supports simultaneous downloads, download queue, selected downloads in torrent package, fast-resume, chatting, disk cache, speed limits, port mapping, proxy, ip-filter, etc.

BitComet Homepage     Download BitComet

BitLord is a BitTorrent client written in C++ for Microsoft Windows. It is an outdated version of the free BitComet client, modified to include advertisements. BitLord is a powerful, clean, fast, and easy-to-use BitTorrent client.

BitLord Homepage     Download BitLord

Transmission is a fast, easy, and free multi-platform BitTorrent client with a focus on being lightweight yet feature-filled. Transmission has been built from the ground up to be a lightweight, yet powerful BitTorrent client. Its simple, intuitive interface is designed to integrate tightly with whatever computing environment you choose to use. Transmission strikes a balance between providing useful functionality without feature bloat. It is also free for anyone to use or modify.

Transmission Homepage     Download Transmission