Here's the email I received:
Twelve Days of Free Frog God!
The holidays are about giving to those you appreciate and Frog God Games appreciates you. Each day from now until December 25th there will be a free PDF from our catalog (regularly priced between 4.99 and 17.99) .For the next 24 hours (give or take) the Slumbering Tsar Part 1 is free to everyone at the Frog God Games website:
No purchase necessary. Simply point your browser to our website and click on the 'Free Downloads' tab to find the daily PDF. The PDF will be available for every system it was released for as of today (Slumbering Tsar was only on Pathfinder). So check your email or the website everyday for another free release until December 25th. Free releases are only available for 24 hours before they return to regular price. The releases can be combined with existing coupons (like the 30% coupon from Humble Bundle or other yet to be announced special offers).