RealNetworks Inc. on Monday launched a Web-based version of its music-subscription service, giving Mac and Linux users access to what had only been available on the PC.

Rhapsody.com is available at no charge for up to 25 songs per month. Subscribers, however, can stream an unlimited number of songs for $9.99 a month from RealNetork's library of more than 1.4 million tunes. For consumers who want to download music to a portable digital player, RealNetworks offers Rhapsody To Go for $14.99 a month.

Before the Web-based service, Rhapsody was only available through software that had to be downloaded and installed on a PC. The new service, which is accessible through a Web browser, means people with Macs of Linux-based computers can also play and share songs through Rhapsody.

In addition, RealNetworks introduced a Web services initiative that enables third-party Web portals and community and music sites and other Web sites to integrate song playback and editorial content from Rhapsody. Available tools make it possible to create links to individual music tracks, full albums and radio stations.

XML feeds, including RSS, make it possible to integrate editorial information, such as new releases, top 10 tracks and top 10 albums.

Coinciding with the new services was the release of a new version of the Rhapsody desktop software for the PC. Rhapsody 3.1 includes several enhancements that make it easier to buy and share music, the Seattle-based company said.

Unlike rival Apple Computer Inc., which only offers pay-to-play music through its online music store iTunes, RealNetworks has been aggressive in offering a subscription service, as well as songs that can be bought to own.

Subscription services are growing in popularity with consumers. JupiterResearch predicts that revenues from the services will surpass that from buy-to-own music by 2009, when revenues are expected to be $900 million and $800 million, respectively.

In four years, music downloaded from the Internet, either through individual purchases or subscription, are expected to account for 12 percent of the $13.5 billion consumers are projected to spend on music, according to JupiterResearch. In 2003, music downloads accounted for 1 percent of the $12 billion spent on music.