What is double invite bug?
Improvements / updates

+1
I totally agree with almost everything @flxhfft is saying.
However, the engine thing is probably taking it too far. It would be amazing, but 1) Chess.com has to develop engines for 4 player chess (Which would be immmensly complicated because there are so many variations -- creating a engine for 4 player chess would take forever), 2) The engine would need a lot of memory to house so many variations, and 3) Some of the creativity will be lost in 4 player chess. Many people would just memorize some computer lines and play those. Also, opening choices will become set instead of debatable because of the engine's choice.
Don't forget, if chess.com makes an engine for 4 player chess, cheating will become a problem. Not everyone has good intentions.
That's probably also why chess.com didn't get computers for variants. You can actually find them online, but chess.com doesn't want cheaters.

Engine implementation wouldn't be hard for chess.com, if they really wanted to. Also openings would not be set as a result of it. The game is too complex to be onesided, and the engines are never going to be good enough to solve it to human advantage. Rather, humans will create complex positions and ideas regardless. Just like in regular chess, there are ways to take the game off the beaten track, without being unsound.
A list of players online, with sorting options for rating, and a friends list, would be helpful.
Castling bug is annoying since you want to play without using it, but then your opponent uses it. Thus, it is part of the game at this point.
Double invite bug is when you invite multiple players to play, and both/all accept. Then the two players will be on team with you, and a clone of yourself. The player inviting is on both teams...
Database search would be nice, but it will hardly be implemented.

Please make a database and full stats like the regular. Thank you for creating this addictive beautiful game.

what is the double invite bug?
i don't think a brute force approch will deliver good results for 4 player. we're gonna have to wait for someone to create a 4player version of leela!

Double invite bug: https://www.chess.com/clubs/forum/view/bug-the-same-player-in-2-teams

^^ flxhfft
I think implementing a chat to find a partner would be good. Also, I think it would be a good idea to have a temporary ban for players who purposefully resign in the first move. Say, for 15 minutes or so. This would help stop players who resign to get a low rating, and would also mean that we higher rated players could safely play without worrying about low rated players resigning on us.
This would only work for teams of course...
First of all, I'd say that the developpers made an amazing work to develop this 4 players chess. In this discussion I think it could be interesting to point out some ideas that could improve the experience. Indeed, I think the community is growing and I think this game is funnier than regular chess because of the teamplay aspect,. Personnaly, I only play in 4pc-teams so my remarks will only concern that part of the game.
1) We need a database ! It would be nice that the games that we played are archived somewhere so we could go back in them and analyze them.
2) A more interactive panel for matchmaking. Like a challenge proposal ; we could propose to play or accept challenges. A panel where we see who propose to play with their rating, etc.
3) A general chat to find teammates. The community in 4pc is big but it is quite difficult to keep up, to see who is online, etc.
4) Maybe it is too much but it would be nice to have an engine we can play against. That way we could improve by playing against very good opponents. Could be nice for analysis as well.
Two points for the gameplay :
5) Maybe don't remove points for disconnecting in the first move of the game ?
6) Fix the castling bug and the double invite bug