eMule is a free peer-to-peer file sharing application for Microsoft Windows. Started in May 2002 as an alternative to eDonkey2000, eMule now connects to both the eDonkey network and the Kad network. The distinguishing features of eMule are the direct exchange of sources between client nodes, fast recovery of corrupted downloads, and the use of a credit system to reward frequent uploaders. Furthermore, eMule transmits data in zlib-compressed form to save bandwidth.

eMule is coded in Microsoft Visual C++ using the Microsoft Foundation Classes. Since July 2002 eMule has been free software, released under the GNU General Public License; its popularity has led to eMule's codebase being used as the basis of a Linux-specific client, xMule, multiplatform clients, aMule and JMule, along with the release of many eMule mods (modifications of the original eMule) on the Internet.

History

The eMule project was started on May 13, 2002 by s (also known as Merkur) who was dissatisfied with the original eDonkey2000 client. Over time more developers joined the effort. The source was first released at version 0.02 and published on SourceForge on July 6, 2002.

eMule was first released as a binary on August 4, 2002 at version 0.05a. The 'Credit System' was implemented for the first time on September 14, 2002 in version 0.19a. The eMule project website started up on December 8, 2002. Since its inception, eMule has been downloaded over 420 million times as of August 5, 2008 making it by far the most downloaded project on SourceForge.

Current versions (v0.40+) of eMule have added support for the Kad network. This network has an implementation of the Kademlia protocol, which does not rely on central servers as the eDonkey network does, but is an implementation of a distributed hash table.

Also added in recent versions were the ability to search using unicode, allowing for searches for files in non-Latin alphabets, and the ability to search servers for files with complete sources of unfinished files on the eDonkey network.

In new versions, a "Bad source list" was added. The application adds an IP address to this list after one unsuccessful connection. After adding an IP to the "Bad source list", the application treats this IP as a "dead" IP. Unavailable IPs are banned for a time period from 15 to 45 minutes. Some users have complained that it leads to a loss of active sources and subsequently slows download speed.

Other recent additions include: the ability to run eMule from a user account with limited privileges (thus enhancing security), and intelligent corruption handling (so that a corrupted chunk does not need to be re-downloaded entirely).

The 0.46b version added the creation and management of "eMule collection" files, which contain a set of links to files intended to be downloaded as a set.

Recently, many ISPs are bandwidth throttling default P2P ports resulting in slow performances. The 0.47b version adds protocol obfuscation; eMule will automatically select two ports at random in the startup wizard.