Android App Deals & Android Apps for Sale
Amazon also offers it via a key card bundled with a $10 Amazon Gift Card for $29.99. (You must add both to your cart to get the discount.) Plus, Prime members bag free shipping. (Non-members can spend over $35 to bag free shipping; otherwise, it adds $4.48.)
The Amazon Appstore also offers it for Android for free. (Google Play has it for the same price.) That's the first time we've seen it for Android for free.
Note that some advanced features require an Office 365 subscription.