From iA wiki
OpenNap is a open-source Napster server, built by DrScholl after reverse engineering the Napster protocol. The next generation of this server is called OpenNap-NG. It has been designed to be run on small connections. (DSL+)
Distributed, it allows admins to form networks like IRC (connections have to be manually allowed on both sides). Searches are routed in a Gnutella-like fashion along the network, responses are sent directly to the searching client. Naturally, OpenNap also removes the limit to MP3 files that the Napster server imposes.
A list of available opennap servers is maintained by Napigator. If your napster client allows it, you can then manually enter the opennap servers address. Otherwise, you can use the original napster client combined with the napigator program (it works by putting an entry into your \windows\hosts file that redirects meta.napster.com to the host you selected in napigator.) Note that Napigator is adware, but does not include any spyware. I am not sure how it is written, but it is perhaps possible to apply the hosts trick to napigator itself, sending the address of the napigator ad-server engine to 127.0.0.1.
(this is not an exhaustive list)
DICE is multi-protocol hybrid server that offers simultaneous connectivity from IRC clients, OpenNap clients, and HTTP clients (WWW browsers). IRC is media of pure chat experience, while OpenNap is directory-publishing service accompanied by chat rooms. HTTP is the best known protocol on the internet to deliver contents to the users. OpenNap-compliant system implemented in DICE is called VirtualDirectory.
In the same way as general web servers offer public interface to file-system, DICE publishes those three unique interfaces to access one object, which is conference space - called channels - shared between users who can communicate one another by their different protocols mutually translated by DICE.
- Jnerve | at Sourceforge - JNerve aims to produce an open source Java implementation of a napster server. Using much of the excellent work already done by the OpenNap project, this project aims to be it's Java counterpart, offering cross-platform compatibility. -- This project has been quiet since the middle of 2000.