What are some alternatives?
When comparing BitTorrent and Shareaza, you can also consider the following products
qBittorrent - Lightweight and open source torrent client that runs on all major platforms.
eMule - eMule is a free peer-to-peer file sharing application for Microsoft Windows.
Transmission - Transmission has the features you expect in a BitTorrent client: encryption, a web-based interface...
RetroShare - RetroShare is a open source cross-platform, private and secure decentralized communication system.
Deluge - Deluge is a full-featured BitTorrent client for Linux, Unix and Windows.
Soulseek - Soulseek® is a unique ad-free, spyware free, and just plain free file sharing application.