The developer of Book of Demons has mentioned that the game will come to Linux after the full Windows release. It looks like a pretty cool take on the action RPG genre.
From the Steam forum post:
Yes, of course it's planned! We want to start working on Linux version after Windows launch.
About the game (Official)
Book of Demons is a deck-building hack and slash adventure game, where players can decide the length of quests. The game is the first installment of Return 2 Games - a series of original mid-core titles, inspired by the early golden days of PC gaming.
It's you who decides the length of quests!
Have only 5 minutes for a game? No problem! Book of Demons allows you to set the length of each quest, thanks to our Flexiscope™ system. It learns your way of playing and always gives you the best experience, making Book of Demons the first truly accessible hack & slash!
Thanks for letting me know Pawel!