From AMule Project FAQ
Kademlia is a serverless network for the *Mule clients.
It is based on the Kademlia algorithm by Petar Maymounkov and David Mazières (New York University, 2002), as described in their paper "Kademlia: A Peer-to-peer Information System Based on the XOR Metric".
The network itself is used as a distributed database of the files and clients on it. The main goal is to provide a reliable, fast, and almost impossible to shutdown way to keep this information. At client to client level, the protocol used for file transfers is shared with the ed2k network at this point, tho this could change in the future.
For information about it you can either read the ED2K-Kademlia FAQ or see eMule's support page.