There are two projects, actually,
One, at https://green.cardsync.xyz/, is a Trello bot that people can just add to their cards and they start syncing. Free accounts get 10 groups of syncing cards, for $19 people can increase that to 50 groups and so on. The other, at https://teams.cardsync.xyz/, is a Trello Power-Up that people can install from their Trello Power-Up menu. It then prompts people to create a bot on their own and register it with the Power-Up, then people can use custom menus that are added to the cards on the boards to which the Power-Up was added to create syncing groups and add cards to these groups. This one uses metered billing.