Minecraft Windows 10 Edition is free for owners of the Java pased version of Minecraft. Here is Mojang's blog post on it.
It requires you to be signed in to Xbox Live to play (this is part of your Microsoft account used to purchase the game).
This means it has Xbox Achievements and Friends built in. Though due to this being far cheaper (more than half the price) of the Java version of the game it does use the console idea of paying for skin packs though these are purely cosmetic.
The game runs very smoothly but it not on par with the Java version in terms of features yet.
