Still no Spotify and still no Apple. But the cloud music market now has yet another entrant in the form of Rdio, a slick social music subscription service that is sure to make waves in the ever-growing competitive landscape. Rdio is the latest company from Kazaa and Skype founders Janus Friis and Niklas Zennstrom.

The basics: on-demand and unlimited access to a catalog of five million songs -- with all the major labels onboard -- that also includes an a la carte option. A $5 per month Web-only tier lets users access all the streaming features via their browser. And for $10 a month, users can download a desktop application (required if they buy a la carte) and access to all the same features, along with caching from a BlackBerry and iPhone app (an Android version in the works). There is no free paid tier.

The Rdio service is not fully live just yet. It's still an invite-only beta, and general availability is not expected until later this year. But this is the first time details of the service have been made public, and if the live version works anything like the short demo, this newcomer shows some real promise.

Like other cloud-based services, Rdio hopes to set itself apart based on its music discovery capabilities, and does so through a decidedly social interface that borrows heavily from Facebook and Twitter.

Users can connect to each other by "following" them, much like on Twitter. If any user you're following adds a new song to their collection, or makes a new playlist, you will see that activity in your feed. Each user profile is set up much like Facebook, where users see a feed of both their own activity and that of their friends.

"It's constantly updating, constantly feeding you new sources of information about music," Rdio CEO Drew Larner says.

Rdio also has a Pandora-like customized radio feature that builds automatic playlists based on a selected artist. It can't, however, build that playlist based off a specific seed song like Pandora does. Other elements include a tool that will scan users' iTunes or windows Media Player libraries and automatically add it to the online collection, shared collaborative playlists, links to share songs and playlists on Facebook and Twitter, and more.

Many of the company's employees hail from Skype, which is reflected by the simple interface and intuitive controls. Rdio certainly has all the right pieces and definitely feels different from other streaming services. Labels have expressed excitement over the launch and seem to have high hopes.

But until it goes fully live, we won't know how well these features work under a critical mass of users, nor whether it will even succeed in getting that critical mass. Details of its marketing and promotional strategy are being held close to the chest. And just because Skype and Kazaa were popular services, not everything Friis and Zennstrom touches turns to gold, as indicated by the failure of their last venture: the Internet video network Joost.