By far the most robust and feature-complete tabletop game engine out there, and the developers are still very actively adding new features and fixing bugs.
Community is quite active, with many game lobbies open at any given time.
Very much user-created Workshop content, you can find several versions of almost any game you could possibly name.
Creation of boards and decks is fairly easy to do yourself, in the rare case of a game being absent from the Workshop.
In a nutshell, $20 to play every tabletop game in existence.