May I suggest the Greenchess website? https://greenchess.net/ It certainly has some huge potential: nice minimalist interface and probably about 50 or 60 chess variants for all tastes. Some of them are obviously more or less "recent". You can easily start a new game or accept a pending invitation. I would call the set of players quite "active" and certainly motivated. But it is true that the pool of players remains small and you generally play against the same players again and again.