Artifact - the Dota-inspired card game in development at Valve - might not be limited to the digital space. According to a recent news post on PCGamesN, Valve has actually trademarked Artifact as a card game using real playing cards.
That doesn't necessarily mean that Valve is looking to actively develop a physical version of Artifact right now though, and it may simply be a case of the company protecting every possible avenue it might want to pursue in the future.
Still, it would be an intriguing development if the company were to go down this route, and not entirely uncommon either. Hearthstone's predecessor was a paper-based collectible card game, after all, and Magic The Gathering has managed to carve out a position for itself online alongside it's much greater presence in the real world.
Were the digital and real-world versions be equivalent to one another, it would place some restrictions on the design space of the former. The more number and stat-juggling work there is to be done typically, the more interesting digital card games can be, but it's tough to transfer some of that randomness into reality.
We'll continue keeping a very close eye on developments of Artifact between now and its anticipated release at some point in 2018. To get up to speed on everything that's currently known about the game, make sure you take a look through our comprehensive Artifact guide.