On Sunday evening, all trading through MusicCity.com's servers was halted; members were sent a pop-up message telling them to download the new client, dubbed Morpheus.
The legal suit that has forced Napster to try to keep its members from sharing copyright-protected files has seen a migration of people to other services based on its technology.
These services, running technology cloned from Napster's servers, known as OpenNap servers, have blossomed in recent months. One of the most popular belonged to MusicCity and typically offered in excess of 20TB (terabytes) of data. At their peak in popularity, Napster's servers offered around 12TB.
MusicCity appears to have attracted a significant number of ex-Napster members to this new client, claiming to already have snagged more than 27,000 people on its first day.
The new client is similar to Napster and other services such as Gnutella in that it searches and lets files flow directly between people, a technique referred to as peer-to-peer. Like Gnutella, Morpheus is designed to enable people to share all kinds of media, not just MP3 files.
It remains unclear, however, how MusicCity intends to make its new technology pay for itself, if it plans to charge individuals, and how it may try to fend off attention from the Recording Industry Association of America, which has caused Napster so much strife. The company has previously committed to keeping the Morpheus client free.
A representative for MusicCity, who describes the company as a start-up, refused to comment on any of these points, saying the company's position would be made clear in coming weeks with the launch of another Morpheus client. The fate of MusicCity's OpenNap servers is "up in the air," the representative added.
The representative did not rule out the possibility that source code behind the technology might be published, allowing a wider community of programmers to contribute to development of its usability and functionality. Morpheus currently runs on Windows only, and although there is a promise of a Linux version at some future date, there is no mention of versions for the Mac and other operating systems.
Staff writer Will Knight reported from London.