It's here!
https://www.chess.com/4-player-chess
I played 4-way chess on this site Sunday and Monday; but I can't find my way back to the entrance today!
Just remember in notes this link: https://www.chess.com/4-player-chess
It is now on chess.com....I prefer teams, but they have it both ways. In teams, the opposite-side player is your partner. Very hard to get a grip on opening moves, as some lead to fast disaster. Higher-rated players sometimes get bossy with partners, and a few are jerks, but the communication can get interesting even when congenial as usual. When a move is suggested, I am rarely sure if it is just an idea worth looking at or one that has been "carefully" vetted (given the fairly short times allowed for moves, and the many pieces, even good players may blunder. )Fun, stressful....most chess principles apply but there are weird developments. Much teamwork is required.
By the way, the free-for-all version is wilder but less stressful. When you mess, up, you don't take your partner down with you. But yes, it is normal strategy for good players to be spectators when they can and lay back to let others kill each other for a while, when they can get away with it. But the solo game uses a point system to determine the winner, based on piece captures, so dodging the action too long can backfire.
We need 4 way chess here to play with friends!