We have had a Chess variants server since 2001. It's called Game Courier, and it supports more Chess variants than all the others combined.
This is what people call a 'turn-based server'. Which is fine for correspondence chess, but incomparable to a real-time server like FICS or LiChess. People play bullet games there, meaning 2 min per game per person, and sub-second recording of thinking time. To play such a game you need to have deposited your move about 1 sec after your opponent did. (And that should then be mostly their own thinking, not the roundtrip delay of the network...)
This is what people call a 'turn-based server'. Which is fine for correspondence chess, but incomparable to a real-time server like FICS or LiChess. People play bullet games there, meaning 2 min per game per person, and sub-second recording of thinking time. To play such a game you need to have deposited your move about 1 sec after your opponent did. (And that should then be mostly their own thinking, not the roundtrip delay of the network...)