Why are open source file sharing applications so popular? The answer to that question may be obvious to some, but the explosion in paid-for, online digital content services in recent years hasn't dented the download rates of free file sharing applications.

At the time of writing, open source software repository SourceForge.net lists the top four downloads of all projects to be related to file sharing. TechWorld takes a look at five open source file sharing applications that can be used for good or evil.

1. Vuze

The file sharing application formerly known as Azureus is SourceForge's most popular project by number of downloads. Vuze.com has morphed Azureus into a content portal where members can share audio, video and game files. Contributors can offer their content for free or make money with it via advertising or online sales.

The Vuze client has an embedded video player with a fullscreen view and videos can be watched as they are downloading. RSS feeds are also a feature. The former Azureus has a well documented wiki-based user guide too.

Home Page: http://www.vuze.com, Licence: GPL Platforms: Linux, Mac OS X and Windows Protocols: BitTorrent

2. Shareaza

Shareaza is a multi-protocol P2P client for Windows, that has chalked up more than 40 million downloads from SourceForge alone. Sharing can occur across more than one type of transfer protocol at a time and multimedia files can be played within the application. Like Vuze, Shareaza can preview downloading files.

Integrated chat can be used to communicate with other file sharers, and the look and feel can be customized with "skins". A skin design tool is also available.

At the time of writing Shareaza is embroiled in a legal dispute over the trademark of its name and is seeking donations.

Home Page: http://shareaza.sourceforge.net Licence: GPL Platforms: Windows Protocols: Gnutella, eDonkey, HTTP, FTP and BitTorrent

3. eMule

The eMule project began as a replacement to the eDonkey2000 P2P client and it now ranks in the top five SourceForge downloads.

eMule's content database keeps track of freely distributable software, like Firefox, downloaded (shared) using its client.

A built-in messaging system and IRC client allows people to chat to others using eMule or other IRC clients. Numerous skins are available for that unique touch.

Home Page: http://www.emule-project.net Licence: GPL Platforms: Windows Protocols: eDonkey, Kademlia