Valve's Artifact Classic card game. I actually found the basic formula to be really fun.
I think this game died for two reasons:
A) The game was review bombed for its monetization (IMO a lot of this was the non-target audience trying it and leaving a bad review)
B) Valve said following the review bombing that they were going to make major changes. This resulted in a lot of Artifact fans (IMO) leaving the game because ... why invested and learn a game that's going to undergo major changes.
So Valve worked on Artifact Foundry (and never finished it) ... before eventually everyone at Valve gave up and released both Artifact Classic and Artifact Foundry for free. The original Artifact Classic is still a great time with a friend and all cards are now totally free so you can build whatever decks you want.
It's basically a AAA studio card game, with cross platform support, released in complete, for free ... because of some poor decision making. Some things may be unbalanced but if you're playing with friends anyways ... just have a friendly agreement to not use the cards that cause problems in your decks. It also could bounce back into active development if it starts to acquire a player base again (because Valve).