Because of strong demand, Spotify has sometimes limited access to its free service to invitation only. Spotify Open offers those without an invite the opportunity to sample the service with a free, ad-supported limited version that offers 20 hours of monthly access to the full music catalog.

Spotify Open may be an experiment for the company. It's a far less costly way to encourage  new users to try the service than the unlimited accesses of Spotify Free. But for now at least, Free is not going away. Spotify says it will continue offer ad supported access to 7 million its European users, and new invitations are readily available, according to the company.

The new Spotify Unlimited offers full ad free access for £4.99 per month on the computer, but without the mobile capability, enhanced sound quality and exclusive content of the more expensive Spotify Premium.

Last month Spotify introduced a number of new features that enabled users to merge music stored on their computer into their Spotify music in the cloud playlist, as well as, more social features via Facebook and Twitter.

Spotify also launched today in the Netherlands.