As Napster collapses slowly into a musical black hole, millions of people who once searched painlessly for free music on the Web are hunting for the next online file-swapping utopia. At least a half-dozen services have picked up large collections of Napster emigres over the past few months. No single service has emerged as a standout that offers the same breadth of obscure music as Napster once did. But many of them are closing in, with hundreds of thousands of people at a time offering their music collections. Interest has spiked in recent weeks as Napster has struggled to remain a viable service while complying with a court order that it block copyrighted music. Adding to the company's woes, it has been offline for several days this week -- forcing traders to look for alternatives. These rivals' rise is bad news for the record and movie industries, which are increasingly focusing their enforcement actions on these new threats. They have already sued Aimster, one of the most vocal foes of the industries' attempts to persuade all file swappers to start filtering files. They've also started targeting the services that lack companies to sue, asking Internet service providers to shut down activity on the OpenNap and Gnutella networks. But trading on those networks has continued. The Recording Industry Association of America (RIAA) says it is working with some of Napster alternatives, hoping to avoid going to courts more than necessary. "We continue to reach out to these other services in the hope that we can work through the legal issues and avoid litigation," said Cary Sherman, the RIAA's general counsel. "If that does not work, we will not shy away from litigation if that's what's necessary." As yet, individuals haven't been targeted for trading large numbers of files through one of these services. But some analysts say it's only a matter of time. The courts have indicated that they believe individuals' file swapping is likely to violate copyright law, though no judge has yet ruled directly on this issue. This publication informally tested six of the most visible Napster alternatives for breadth of offerings, ease of use and other features. The conclusion: File-swapping is alive and well on the Internet for now. As the reviews below show, most of the leading file-swapping services have evolved to the point where they offer almost the same features. Only a few limit their searches to audio files, and network-watchers say more videos are being traded. Most have added features that allow downloads to pick up again after they've been interrupted, and a few have created technology that allows people to download files from several places at the same time, speeding and stabilizing downloads. Many of the services, desperate for a revenue stream, also are adding extra software that pops up unrelated ads when a surfer is on the Web or otherwise tracks someone's activity online. This can be inconvenient and can slow or crash computers. On the whole, however, the review of the services found that most of the alternatives are comparable, showing only small differences in ease of use and in the number of files actually available at a given time. Methodology: We downloaded each of the leading applications, installed them on IBM Thinkpad laptop computers running Windows 2000, and searched for five relatively popular songs from several genres. The songs were "Enter Sandman" by Metallica, "Don't Let Me Be The Last To Know" by Britney Spears, "Let it Be" by the Beatles, "Giant Steps" by John Coltrane, and "Moonlight Sonata" by Ludwig van Beethoven. All of the applications varied widely when searching for more obscure songs. All the searches were done between 8am and 5pm PDT and were performed at least twice over the period of a week. Because the number of people on any given service fluctuates dramatically from hour to hour and day to day -- which in turn changes the songs available for download -- this guide should be viewed as only a typical snapshot and not the final word on what is available through the services. The number of users was taken from the company or from the software itself, when this information was available. Third-party estimates are noted when included. In several cases, comments are included from individuals who have spent considerable time using a given service and were able to bring out points that shed more light on a side-by-side test. Aimster

• Headquarters: Troy, New York state
• Launch date: August 2000
• Type of service: central server
• Latest version: Aimster 3.229
• Number of simultaneous users: 200,000
• Types of files supported: any media file

Aimster is the bomb-thrower among today's crop of file swappers. It has retained its original mission of letting people trade files among the "buddies" in their instant messaging lists, but it's also added a Napster-like option that can search hundreds of thousands of computers at once. That's drawn a lawsuit from record labels, but Aimster is so far holding firm against filtering songs. The interface is fairly easy to use, although the sign-up process can be a little confusing. The service is one of the only ones to support Macintosh and Windows computers. It also installs software that continues to run in the background after closing Aimster itself, but this can be shut down fairly easily. Audiogalaxy

• Headquarters: Austin, Texas
• Launch date: October 1999
• Type of service: central server
• Latest version: Audiogalaxy Satellite .606
• Number of simultaneous users: not available
• Types of files supported: audio

Audiogalaxy's application is easy to use with its simple text search. The "satellite" application, which lets someone search other people's hard drives, runs in the background after it has loaded. The Web page also allows searches of FTP sites. Audiogalaxy has an auto-resume function so that it automatically continues a download if there is an interruption. The application has recently suffered under high levels of traffic, slowing or stalling some searches. Audiogalaxy has begun working with copyright holders to block songs, but the filters are in an early stage that allow misspellings, such as "Metalica" instead of "Metallica," to get through. It also installs a software program called "Webhancer" that tracks individuals' Internet connections and reports them, without identifying information, to another company. Gnutella Network

• Most popular software: BearShare; LimeWire
• Headquarters: BearShare: Florida; LimeWire: New York
• Launch date: BearShare: December 2000; LimeWire: August 2000
• Type of service: pure peer-to-peer
• Latest version: BearShare 2.2.5; LimeWire 1.4b
• Number of simultaneous users (Gnutella Network): 44,266 on 7/03/01 at 12.37pm PDT (from Clip2.com)
• Types of files supported: any

Gnutella, which lacks any central company or servers keeping its users in line, has always been a little wilder than Napster. BearShare and LimeWire have taken much of the difficulty out of the service. They're still a little harder to understand than some alternative services, since both show detailed information about what connections are being made and dropped. But if people ignore what they don't understand, it's easy to search for any kind of media. Advanced LimeWire and BearShare users can set the amount of bandwidth taken up by others' connections to their computer. All Gnutella clients include a "monitor" feature that shows what other people on the network are searching for, a sometimes sobering look at online psychology. BearShare includes extra "adware" software with its download, but careful people can simply not install this or disable it when it starts up. Because any file is supported, people should be careful that what they are downloading are not viruses masquerading as music or video files. "You get booted a lot from what you are downloading, particularly if you are downloading more than one file at a time. It's also a little goofy to use... it takes a little getting used to." -- Michael Folkman, Spokane, Washington. iMesh

• Headquarters: Israel
• Launch date: founded 1999
• Type of service: central server
• Latest version: 2.20 beta iMesh
• Number of simultaneous users: 300,000
• Types of files supported: all media files

iMesh is one of the oldest file-swapping services, one of the few first-generation companies to stay running when Napster started having legal troubles. It's spent considerable time upgrading its technology and has a fairly intuitive interface. Seriously obscure songs will show up, although occasionally searches must be tried several times with different keywords to find even the most common songs. Server loads have reached the point where delays are possible. The software supports an auto-resume feature. The company has said for months that it would begin filtering songs at the record industry's request, but no blocks have shown up yet. The company distributes bundled ad software that can be annoying and draining on computer resources and which can be difficult to uninstall. "I can find things on iMesh that I can't find on other networks... Sometimes it is a little slow though." -- Zohair Karim, Orlando, Florida. Napster

• Headquarters: Redwood City, California
• Launch date: June 1999
• Type of service: central server
• Latest version: Napster 2.0 beta 10.3 for Windows; Napster 1.0 beta 1.1 for Mac
• Number of simultaneous users: 150,000
• Types of files supported: audio

Napster is the granddaddy of music file swapping, even if it's not the oldest or the purest peer-to-peer model. Its interface has taken a few bruises from critics, but it is easy to download, install and use. Basic text boxes make it simple even for beginners to search by title, artist or both. The service denotes files as having slow or fast connections to the Net, driving people toward the faster connections. But there is a downside. After once having virtually any song imaginable on the service, filters have made most songs hard to find. A new version intended to loosen the filters somewhat instead blocks most music and will likely do so until the company works out its bugs. The company has said the free version will be replaced by a paid subscription service sometime in the summer of 2001. "The new beta is, at best, an elaborate chat program. It's a great place to meet with other online music downloaders to discuss where to go next to get the goods. But it's not Napster." -- Josh Howard, Temecula, California OpenNap Network (accessed through Napigator software)

• Headquarters: not applicable
• Launch date: January 2000
• Type of service: scattered, unconnected central servers
• Latest version: Napigator .41
• Number of simultaneous users: 82,314 at 6/28/01 10:31am PDT (from Clip2.com)
• Types of files supported: any media type

Not long after Napster reached the public spotlight, a group of intrepid programmers figured out how it worked and released the information to the public. The result was the OpenNap Network, a way for ordinary people to create their own file-swapping hubs that use Napster technology but have nothing else to do with the company. Many of these hubs pop up and down around the world, and are typically found and indexed with the Napigator software. This piggybacks on the ordinary Napster program, and so the interface is identical. It is fairly easy to decide which server to choose -- clicking on the Napigator button brings up a list that shows how many people are on each one. The number of people in any single OpenNap server is much lower than the rival file-swappers, ranging from about 3,500 on down. That generally means fewer songs are available. But the independent nature of the network means it probably won't disappear anytime soon. Kazaa -- MusicCity Morpheus

• Headquarters: Kazaa: Amsterdam, Netherlands; MusicCity: Nashville, Tennessee
• Launch date: Kazaa: July 2000; MusicCity Morpheus: April 2001
• Type of service: peer-to-peer
• Latest version: MusicCity Preview; Kazaa Media Desktop 1.2
• Number of simultaneous users (joint network): 313,587 on 6/28/01 at 10.12am PDT (from Clip2.com)
• Types of files supported: any media type

MusicCity and Kazaa's Morpheus tap into the same network, with software created by a Dutch company and licensed to MusicCity. Together they represent one of the most advanced peer-to-peer networks, with a decentralised approach somewhat similar to Gnutella. The software includes instant messaging, a media player and a file manager for creating playlists. The application can download files from several sources at once -- creating a faster or more stable download than some rivals -- and allows downloads to pick up where they left off if interrupted. The interface is easy to use, with options for breaking down a search by media type or following up searches with "same artist" or "same album". The Kazaa software limits MP3 files to 128kbps, or slightly less than CD quality, but MusicCity has no such filters. MusicCity plans to release a new version of its Morpheus software soon, which will include links to other peer-to-peer networks and additional communications features. "There seems to be many more downloadable files on Morpheus than from other programs... I have found that there is less time used in searching and less time used in finding an available user/server to get it from." -- David Lu, Cincinnati The Internet is changing the face of the music industry forever. Find out more in ZDNet UK's MP3 News Section. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Napster Debate. Let the editors know what you think in the Mailroom. And read other letters.