I think Lichess is the best, and I have read that it is only maintained by one person.
I agree, I use lichess - but the question was, where can we play these modes.
I found pawn-back to be the most interesting just from the changes to existing chess logic. Pawn-back resulted in the most change in piece-value from classical and during simulations were used 100% of the time.
Re:Reimagining Chess with AlphaZero
by SubiculumCode on Monday January 31, 2022 @11:32AM
(#30149878)
No castling? Okay, 1.D4 it is.
Chess.com currently supports most of the modes in the list - except, I think, semi-torpedo, no-castling (10), and pawn-back. Which, to me, are the least exciting mods anyway.