Sony just opened up a sign up page for a beta of their PlayStation Now service, although signing up does not guarantee beta access. Sony hopes to have the full service implemented by Summer of 2014. This announcement of this service caused GameStop's stock value to fall.
Several years ago, Sony acquired Gaiki, a company that created technology designed to run video games on separate platform and then stream a video of the game on a device that might not ordinary be capable of running those video games. It also allows users to access games without going through the trouble of downloading or installing them.
Last year, Sony announced that they would use this technology to make PlayStation 3, PlayStation 2, and PS1 games playable on PS4. The service will also be available on PlayStation 3 and PS4 at launch, and will later expand Sony Vita, BRAVIA TV, and other non-Sony devices. PlayStation 3 games will be supported at launch.
Games will be streamed at 720p resolution. Game saves will be stored online, allowing you to resume play later. PlayStation Now supports multiplayer, including multiplayer against other people who are playing retail copies of the games through the PlayStation 3. Sony has not announced whether or not this service will require PlayStation Plus, or if having PlayStation plus will enable you to receive discounts on the service. The games that can be played on PlayStation now have not been announced yet.
This service enables players to either rent games, or pay a subscription fee to gain access an unspecified number of games. Due to the nature of the service, there has not been any word on a permanent buying option. Sony also only plans to launch the service in North America at the moment, and does not have a date for when it will be released in other regions.