Windows 10 @Bay Trail. Lenovo demands exorbitant 350 Euros for the Ideapad Miix 300-10IBY that was kindly provided to us. That is a lot of money for an older CPU and middling battery life. However, some lower-priced models also exist.
http://www.notebookcheck.net/Lenovo-IdeaPad-Miix-300-10IBY-Convertible-Review.159389.0.html