Magento released Magento 2 Developer Beta yesterday on 17th December. And we have been playing since then.
Here is a Demostore for Magento 2 Developer beta to play around.
Front-End: http://www.magecomp.com/magento-2-beta-demostore/
Back-End: http://www.magecomp.com/magento-2-beta-demostore/admin
username: admin
password: test123