Anyone that bought Google Glass became eligible for using the Mirror API for Google Glass. Google only wanted developers with access to the Google Glass hardware to develop for the device at the time. But over the weekend, Google has opened up the Mirror API for everyone. The Mirror API lets developers push and pull information to and from the device and then show it on a card interface. This method works well for news apps and social networks.
[Source: TechCrunch/Google Developers on Google+]