NERTS! Online - Making Solitaire Cool

This is a game I spent way longer playing than I had ever expected to when first installing it. NERTS online is just free-to-play competitive solitaire. All the rules are the same as when playing solo, but everyone playing shares the same pool for placing cards. When a player's set of face-down cards is empty they can call NERTS, forcing everyone to gain points for every card placed into the pool and lose points for every card left in their corner pile. It's such a simple concept, but the game is incredibly addicting and well made, likely owing to its developer being Zachtronics of Infinifactory fame. 

I'm not kidding when I say NERTS has been responsible for some of the most tense gameplay experiences I've had in a while. And as I mentioned at the start, the game is 100% free. You can unlock different card backs by purchasing other Zachtronics games, but otherwise there's no monetization whatsoever. If you know the rules of solitaire this is a game I think just about everyone should try at least once just for the novelty. Who knows? You may wind up loving it as much as I have.